Few plants are as medicinally, culturally, and economically important as the sandalwoods, commonly known for their aromatic heartwood oil. The sandalwoods comprise the small genus of shrubs and trees, Santalum L. (Santalaceae), which is widely distributed throughout India, Australia, and the Pacific Islands (Harbaugh 2007; Harbaugh and Baldwin 2007). More than a quarter of the currently recognized sandalwood species occur in the Hawaiian Islands, where it is known locally by its Hawaiian name ‘iliahi. Hawaiian sandalwoods have a long history of traditional ethnobotanical uses, and have a prominent contribution to the cultural and economic history of the islands. The grated wood and oil has been used to scent and waterproof kapa (barkcloth) (St. John 1947; Merlin and VanRavenswaay 1990), the wood used as firewood and to treat sores (Merlin and VanRavenswaay 1990) and urogenital diseases (Brennan and Merlin 1991), as well as carved into the musical instrument ‘ukeke (Buck 1964). Demand for their valuable products has led to drastic over-harvesting of sandalwoods, and now they are among the most heavily exploited groups of plants across their range (Merlin and VanRavenswaay 1990). The early 19th century in the Hawaiian Islands is known as the “Sandalwood Era,” where it is estimated that as many as 90% of Hawaiian sandalwood trees were felled and exchanged for ships and supplies (Shineberg 1967; Kepler 1998). As a result, most Hawaiian sandalwood taxa are now rare or threatened, and one variety, Santalum freycinetianum Gaudich. var. lanaiense Rock is currently listed as endangered (Herbst 1986; Merlin and VanRavenswaay 1990). A single known species, S. fernandezianum F. Phil, from the Juan Fernandez Islands, has gone extinct due to human exploitation in the last century (Stuessy et al. 1992), and a number of other Santalum taxa, including several in the Hawaiian Islands described in this paper may warrant listing before they have a similar fate.

There have been a number of taxonomic treatments of the Hawaiian sandalwoods, starting with the description by Gaudichaud-Beaupré in 1829 of two species, the red-flowered S. freycinetianum Gaudich. and white-flowered S. ellipticum Gaudich. Reconstruction of the Santalum phylogeny has demonstrated that the Hawaiian sandalwoods are the result of two independent colonization events from Australia (Harbaugh and Baldwin 2007; Harbaugh 2008), which correspond to the red-flowered (section Solenantha Tuyama) and white-flowered (section Hawaiiensia Skottsb.) species. Tuyama (1939) separated the Hawaiian members of section Santalum into the endemic section Solenantha based on their longer perianth tubes, smaller ovaries, and absence of hairs proximal to the filaments. Section Hawaiiensia is characterized as having white, green, brown, or orange corollas that are as wide as long, and inferior ovaries (Skottsberg 1930; Stemmermann 1980a; Wagner et al. 1999b).

Subsequent treatments, including those by Gray (1860), Hillebrand (1888), Rock (1916), Skottsberg (1927), Stemmermann (1980a), and St. John (1984), have revealed a number of additional species within these two lineages. Wagner et al. (1999b) based their treatment on the revision by Stemmermann (1980a), which recognizes four named species, two in the white-flowered group (S. ellipticum and S. paniculatum Hook. & Arn.) and two in the red-flowered group (S. freycinetianum and S. haleakalae Hillebr.), with an additional three varieties (S. freycinetianum vars. lanaiense and pyrularium (A. Gray) Stemmerm., and S. paniculatum var. pilgeri (Rock) Stemmerm.). Several taxa described by St. John in his 1984 revision, including S. majus H. St. John and S. involutum H. St. John, were not recognized as distinct from S. freycinetianum var. pyrularium by Wagner et al. (1999b).

Despite the number of taxonomic treatments that have focused on Hawaiian sandalwood there remains considerable confusion on how to apply the names to certain populations, especially for the red-flowered taxa, S. haleakalae and S. freycinetianum. This is because the “distinction between taxa is often not clear-cut” (Stemmermann 1980a), and there is considerable morphological diversity within their ranges, and even within populations. Another potential issue is whether to treat weakly distinct populations on different islands as separate species. This issue is common for many morphologically-based Hawaiian classifications and recent studies involving morphological data in conjunction with molecular data have shown that not only are morphologically similar populations on different islands sometimes distinct species (e.g. Schiedea), but there may be more cryptic species than could be distinguished using morphology alone (e.g. Dubautia see Baldwin and Friar 2010). An example of this taxonomic confusion in regard to Santalum is how to assign variable populations of S. freycinetianum var. lanaiense, which has implications for its conservation. It is unclear whether the populations of S. freycinetianum on West Maui should be assigned to the endangered var. lanaiense, also found on Lana‘i, or to var. freycinetianum, which occurs on O‘ahu and Moloka‘i. The lower elevation plants of Haleakala on East Maui have also been assigned to var. lanaiense (Wagner et al. 1999b); Stemmermann (1980a) circumscribed these plants as a new and restricted variety, S. freycinetianum Gaudich. var. auwahiense Stemmerm. Albeit, according to Stemmermann (1980a, 1980b), these plants may form a continuum in a number of morphological characters from the upper elevation plants from Haleakala, which have been considered a distinct species, S. haleakalae.

In this study we employ several new lines of evidence to investigate the morphological and genetic variation within and between populations of S. freycinetianum and S. haleakalae to answer the following questions: 1) Should the red-flowered S. freycinetianum be split into multiple varieties, or regarded as one variable species? 2) If the varieties are supported as distinct, are there characters or evidence to help delimit the endangered S. freycinetianum var. lanaiense? 3) Should S. haleakalae be considered as a separate species, or a variety of S. freycinetianum? 4) Should S. freycinetianum var. pyrularium on Kaua‘i be considered as a separate species? 5) What were the patterns of colonization of the red-flowered sandalwoods in the Hawaiian Islands?

In past research, DNA sequence data were insufficient to completely resolve the relationships within S. freycinetianum and S. haleakalae (Harbaugh and Baldwin 2007; Harbaugh 2008). Therefore in this study, in addition to an expanded phylogenetic analysis based on nrDNA (ITS, ETS) and cpDNA (3′ trnK intron) sequences, evidence is integrated from two novel sources including a Bayesian STRUCTURE analysis using microsatellites, as well as a morphological analysis of 28 quantitative and qualitative characters. Microsatellite data have been chosen for the present study because they have high mutation rates and polymorphism, and are good to determine population genetic diversity and structure in taxa that have recently diverged, such as in island archipelagos (Zhang and Hewitt 2003; Butaud et al. 2005; Lhuillier et al. 2006a).

MATERIALS AND METHODS

Phylogenetic Analysis We sequenced a total of 42 specimens in this study, 17 of which were outgroup specimens including one of Colpoon Berg, and the remaining were Santalum specimens based on previous analyses (Harbaugh and Baldwin 2007; Harbaugh 2008). Twenty-five accessions of S. freycinetianum and S. haleakalae were selected as the ingroup from across the morphological diversity of these taxa from across their natural ranges in the Hawaiian Islands. For each specimen, the internal transcribed spacer (ITS) and external transcribed spacer (ETS) regions of 18S–26S nrDNA, as well as the cpDNA3′ trnK intron were sequenced from genomic DNA extracted from silica-dried leaf material and herbarium specimens using the same primers and methods described in Harbaugh and Baldwin (2007). See Appendix 1 for locality and herbarium voucher information, as well as GenBank accession numbers for ITS, ETS, and 3′ trnK intron sequences for all specimens used in this study.

Nuclear ribosomal and cpDNA matrices were aligned by eye and were not combined, based on the evidence for several instances of hybridization within the genus. A maximum likelihood (ML) analysis was performed using the web-based program RAxML (Stamatakis et al. 2005) with the GTR model of base substitution and gamma model of rate heterogeneity with 1,000 bootstrap replicates (Stamatakis et al. 2008). All identical sequences were removed prior to performing the analyses, leaving a total of 28 sequences in the final aligned nrDNA matrix. The ML analyses were each performed two times (with identical results) to ensure the stability of the topology. Additionally, a maximum parsimony (MP) analysis was performed on each dataset. Insertions and deletions (indels) were not coded as characters as they were in Harbaugh and Baldwin (2007) due to the lack of parsimony informative indels within the ingroup. For the nrDNA data set, which has 150 out of 1,101 bp parsimony informative, a heuristic search was performed in PAUP* 4.0b10 (Swofford 2002) with 10,000 random-addition sequences, TBR branch swapping, and MulTrees on. For the smaller cpDNA dataset, with only five out of 413 bp parsimony informative, an exhaustive search was performed in PAUP*. Parsimony bootstrap values were calculated for the nrDNA data sets using PAUP* using a full heuristic search, with 1,000 bootstrap replicates, 10,000 random-addition sequences, TBR branch swapping, and MulTrees on. Lastly, decay index values were estimated on the nrDNA data set by reiterating the MP analyses holding trees one step longer in successive runs, and comparing the consensus phylogenies.

Microsatellite Analysis—A total of 175 individuals were genotyped in this study using microsatellites (see Appendix 2 for locality and herbarium voucher information). This sampling encompasses representatives of S. freycinetianum and S. haleakalae from multiple populations across the ranges of each taxon. For all samples, total DNA was extracted from silicadried leaf material using either a DNeasy plant mini kit (Qiagen) by hand or using the BioSprint 96 (Qiagen) robotic workstation.

Four polymorphic microsatellite loci were amplified for all 175 specimens using previously published primers, which included three nuclear microsatellites (mSiCIR33, mSiCIR139, and mSiCIR153) that were developed for S. insulare Bert. ex. A. DC. (Lhuillier et al. 2006b), as well as one cpDNAmicrosatellite (NTCP9; Bryan et al. 1999; Butaud et al. 2005). Amplifications were performed in a 10 µL volume [1 µL 10 × buffer (Applied Biosystems), 1 µL 10 µM dNTPs, 0.6 µL, MgCl₂, 0.1 µL Taq DNA polymerase (Applied Biosystems), 0.5 µL of each primer (forward and reverse), and 1 µL DNA template] using a PT-100 thermal cycler (MJ Research, Waltham Massachusetts) under the following polymerase chain reaction (PCR) parameters: 94°C for 5 min followed by 30 cycles of 92°C for 45 sec, annealing temperature (Lhuillier et al. 2006b) for 45 sec, and 72°C for 1 min. The cycling ended with 72°C for 8 min, and then held at 6°C. Forward primers were fluorescently labeled on their 5′ end with either Hex or Fam dyes (Sigma-Aldrich). Labeled PCR products were analyzed in an ABI capillary sequencing machine (Applied Biosystems) using Rox standard (Applied Biosystems). Electropherograms were analyzed using GENESCAN version 2.1 software (Applied Biosystems) and allele sizes were scored using GENOTYPER version 2.5 software (Applied Biosystems).

We used the Bayesian algorithm as implemented by the computer program STRUCTURE version 2.2 (Pritchard et al. 2007) to define genetic groups within S. freycinetianum and S. haleakalae from across their ranges in the Hawaiian Islands. A similar method was used to determine the genetic structure of North American sunflowers (Harter et al. 2004) and Hawaiian Metrosideros (Harbaugh et al. 2009). This algorithm infers genetic discontinuities from individual multilocus genotypes without any a priori knowledge of geographic location or taxonomy. The default settings of the program were used, including an admixture model. To determine the most likely number of groups (K) in the data, a series of analyses were performed from K = 1–20, using 40,000 burn-in and 100,000 repetitions, with ten iterations per K. These results were examined using the ΔK method (Evanno et al. 2005) to identify the most likely number of groups in the data, which in this study was determined unequivocally to be K = 2. At K = 2, a more thorough analysis was performed, using 100,000 burn-in and 1,000,000 repetitions, with only one iteration.

Morphological Analysis —A total of 28 qualitative and quantitative vegetative, floral, and fruit morphological characters were scored on representative herbarium specimens, including type material; many of the specimens that were examined were also used in the molecular analyses. For quantitative characters, measurements were taken from up to three randomly selected parts of interest. The characters that were scored are listed in Table 1, and the specimens examined are indicated with an asterisk in the species descriptions in the Taxonomic Treatment section of this paper. For populations with multiple specimens available, up to five specimens from each population were examined. This was performed to identify potential taxonomic characters that delimit taxa, as well as document the morphological variation within and between taxa, as well as within populations.

RESULTS

Phylogenetic Analysis—The results of the ML and MP analyses are consistent, with the nrDNA tree (Fig. 1; ML: -lnL = 4,171.30, L = 0.1630; MP: No. trees = 24, L = 556, CI = 0.0.840, RI = 0.792; TreeBASE study number S10609) and better resolved than the cpDNA tree (not shown). In the nrDNA phylogeny (Fig. 1), there is little resolution within S. freycinetianum and S. haleakalae from O‘ahu, Lana‘i, Maui, and Moloka‘i, due to a lack of variable characters; S. haleakalae var. haleakalae and most specimens of var. lanaiense group together in a very weakly supported clade, while S. freycinetianum and the remaining specimens of S. haleakalae var. lanaiense are in a polytomy that includes the S. insulare, S. boninense, and S. pyrularium clade. Santalum freycinetianum var. pyrularium is distinct and supported as nested within a clade including S. insulare (French Polynesia; sect. Polynesica Skottsb.) and S. boninense (Bonin Island; sect. Santalum Skottsb.); morphological characteristics, namely of the floral color (cream, greenish to purple) also differentiate it from the other red-flowered taxa in sect. Solenantha. Additionally, several specimens from in and around Kalalau Valley, Kaua‘i, which have been recognized within S. pyrularium, constitute a distinct lineage placed in a clade with white-flowered S. ellipticum and S. paniculatum (sect. Hawaiiensia) in cpDNA and nrDNA trees and shares at least three nrDNA mutations with the red-flowered clade, which predate the split of S. pyrularium. Although this genetically distinct lineage has most recently been treated as S. pyrularium, cryptic morphological characteristics namely of the leaves (see taxonomic treatment below) correspond to the previously recognized taxon described by St. John (1984), S. involutum H. St. John, although characteristics of the floral color and ovary position align it with section Hawaiiensia.

TABLE 1.

The morphological characters of Santalum specimens examined in this study. Characters are identified as being either qualitative or quantitative.

The cpDNAtree (not shown; MP: -lnL = 685.07 and length = 0.0197; MP: No. trees = 6, L = 29, CI = 0.931, RI = 0.724) is mostly consistent with the nrDNA tree, but not well-supported. All accessions of S. freycinetianum and S. haleakalae from O‘ahu, W. Maui, E. Maui, Moloka‘i, and Lana‘i, as well as S. insulare var. raiateense (J. W. Moore) Fosberg & Sachet have identical sequences. In another group of identical sequences are all accessions of S. paniculatum, S. ellipticum, and S. boninense. In the cpDNA tree, individuals of S. pyrularium from Kaua‘i are identical to the S. freycinetianum and S. haeakalae sequences from O‘ahu and Maui Nui, however the individuals from the Na Pali coast and valleys of northern Kaua‘i, which are now considered S. involutum, are identical to S. paniculatum and S. ellipticum, consistent with the results of the nrDNA tree. There is also evidence for more recent hybridization between these two clades; one individual from Kaua‘i (Wood and Perlman 3023 [PTBG]) which is considered morphologically to be S. pyrularium and sympatric with S. ellipticum, has polymorphic nrDNA sequences indicating a hybridization event between S. pyrularium and S. ellipticum, was identical to S. paniculatum and S. ellipticum in its cpDNA sequence.

Microsatellite Analysis—The four polymorphic microsatellite loci that were genotyped in this study have a range of allele numbers, including: three (mSiCIR139; 204–320 bp), five (NTCP9; 287–292 bp), six (mSiCIR153; 283–301), and 17 (mSiCIR33; 204–320). All four loci were successfully genotyped from all 175 specimens included in this study.

The results from the STRUCTURE analysis (see Supplementary Appendix online for data), which identified two distinct genetic groups in Hawaiian Santalum, are shown in Fig. 2. Although there is limited resolution in the microsatellite data, there are several important results that are elucidated. The first is that all specimens from from Moloka‘i, W. Maui, E. Maui, and Lana‘i occur in the same group, and are separate from all specimens from O‘ahu. The other important result of the microsatellite data is that specimens of S. pyrularium are treated in a separate group from S. involutum. These data also place S. pyrularium in a group with S. haleakalae. Lastly, S. involutum is placed in the same group as S. freycinetianum, and not with S. pyrularium.

Morphological Analysis—Results from the morphological analysis reveal that a number of characters scored in this study (Table 1) are not taxonomically useful. Some of these characters are consistent amon all taxa, such as floral tube shape, pedicel length, number of stigma lobes, seed surface texture, and drupe shape. Other characters, such as the disk lobe shape, are not useful as they vary widely within each taxon, and often within a single specimen.

FIG. 1.

The nrDNA (ITS + ETS) Santalum phylogeny. The ML and MP strict consensus phylogeny are congruent and shown here, with ML bootstrap values (> 50%) above and MP bootstrap values (> 50%) and decay index below the branches. Specific taxon, locality, and voucher information for all specimens are listed in Appendix 1, with corresponding sample numbers after taxon names. The revised classification of Santalum taxa featured in this study are in bold, while the old names are beside them in parentheses. The red- and white-flowered groups, as referred to in the text, are indicated on the phylogeny. Additionally, black boxes or white circles on the branches indicate the hypothesized branches on which the progenitors of the hybrid species S. involutum and S. boninense occurred.

DISCUSSION

The goals of this study were to elucidate the genetic structure within and between populations of the Hawaiian redflowered sandalwoods to guide a new classification that reflects evolutionary history and gene flow. Based on the molecular data gathered here, and confirmed by the morphological analyses presented below, there are four important revisions that are warranted: 1) S. freycinetianum is restricted to O‘ahu; 2) S. haleakalae now includes var. haleakalae on East Maui, as well as var. lanaiense, the latter includes populations on East Maui, West Maui, Moloka‘i, and Lana‘i; 3) S. freycinetianum var. pyrularium from Kaua‘i should be considered S. pyrularium; and finally, 4) a set of small populations in and around Kalalau Valley, Kaua‘i, should be regarded as a distinct species, S. involutum, an ancient hybrid between the white and red-flowered Hawaiian Santalum clades. Photos of each taxon are shown in Fig. 3.

Biogeography — The results from the current study suggest that the initial colonization event of Santalum from Australia to the Hawaiian Islands occurred in the island of Kaua‘i, approximately 1.0–1.5 million years ago (Ma; Harbaugh and Baldwin 2007). This first colonizer likely soon dispersed to the neighboring island of O‘ahu sometime after and resulted in a single species, S. freycinetianum. Subsequently, a colonization from O‘ahu to the Maui Nui complex occurred prior to the separation of the Maui Nui complex, in which the islands of Maui, Lana‘i, Moloka‘i, and Kaho‘olawe were connected as a single landmass, which began to break apart approximately 0.6 Ma, but after the island of Moloka‘i was separated from O‘ahu, which was briefly connected via the Penguin Bank shoal until about 2 Ma (Price and Elliott-Fisk 2004); this colonization resulted in S. haleakalae including varieties haleakalae and lanaiense, which occurs throughout all island once included in the Maui Nui complex.

FIG. 2.

Genetic STRUCTURE bar graph of Santalum microsatellite data. Each of the 175 individuals genotyped in this study is represented by a single vertical bar partitioned into two colored segments which represents the individuals probability of belonging to one of two (K = 2) groups. “Group 1” is represented in black, while “Group 2” is represented in grey. Along the top of the bar graph, the five taxa are indicated, while general localities are given below the graph. The order of individuals follows specimens listed in Appendix 2, which also includes detailed voucher and locality information.

The second Santalum colonist arrived to the islands approximately 04–0.6 Ma (Harbaugh and Baldwin 2007) and led to the white-flowered S. ellipticum/S. paniculatum clade. This colonization likely also occurred on Kaua‘i, as there was an ancient hybridization event forming the restricted Kaua‘i endemic S. involutum between the ancestor of each Hawaiian Santalum clade, as indicated by the black squares in Fig. 1. Likely within less than 0.4–0.6 Ma (Harbaugh and Baldwin 2007), S. pyrularium diverged in Kauai from the original colonizing lineage. After this time, the endemic Bonin Island species S. boninense (Bonin Islands) also formed on Kaua‘i as a hybrid event between S. pyrularium and the S. ellipticum/S. paniculatum clade (Harbaugh 2008), indicated by the white circles on Fig. 1. Lastly, the ancestor of S. pyrularium also dispersed out of Kaua‘i southwards to French Polynesia, leading to the variable species S. insulare (Harbaugh and Baldwin 2007).

FIG. 3.

A–B. Santalum haleakalae var. lanaiense, Auwahi Preserve, E. Maui. C. S. haleakalae var. lanaiense, Kanepu‘u Preserve, Lana‘i. D. S. haleakalae var. haleakalae, Haleakala National Park, E. Maui. E. S. haleakalae var. lanaiense, Kamakou Preserve, Moloka‘i F. S. freycinetianum Ko‘olau Mts., O‘ahu. G. S. freycinetianum, Wa‘nae Mts., O‘ahu. H. S. involutum, above Kalalau Valley, Kaua‘i. I. S. pyrularium, Na Pali Kona Forest Reserve, Kaua‘i. J. S. pyrularium, Waimea Canyon State Park. White scale bars (photos B–G and I–J) = 7 mm. All photos taken by D. T. Harbaugh except photo H by K. Wood.

TAXONOMIC TREATMENT

The specimens observed and characterized in this taxonomic treatment were carefully chosen to represent the extent of the natural ranges and morphological diversity of each taxon. The specimens indicated with an asterisk were those specimens for which a more extensive quantitative and qualitative morphological analysis was performed using the characters listed in Table 1. Photos of each taxon are shown in Fig. 3.

SANTALUM FREYCINETIANUM Gaudich. Voy. Uranie, part 11: 442. 1829.—TYPE: U. S. A. Hawaiian Islands: Insulis Sandwichensibus (Wahou), alt. 350–400 hex. 1817, C. Gaudichaud-Beaupré s. n. (holotype: P!; isotypes: B-photo! K-fragment!).

Santalum longifolium Meurisse, Bull. Mens. Soc. Linn. Paris 2: 1026. 1892. Santalum freycinetianum Gaudich. var. longifolium (Meurisse) O.Deg., Flora Hawaiiensis: 100. 1937.—TYPE: U. S. A. Hawaiian Islands: O‘ahu, 1854–55, J. Remy 510 (holotype: P!).

Tree, or shrubby tree, evergreen, usually 4–10 m (rarely up to 20 m) in height, with a single or multiple stems; leaves opposite, more glaucous abaxially, light to dark green, chartaceous, surface not much paler on abaxial side, conduplicatefalcate, narrowly elliptic, oblong, to narrowly ovate, often appearing wilted, (4.1-)5.5–7.9(-10.1) cm long × (1.2-)1.6–3.3(-4.4) cm wide, margins flat (rarely wavy), apices acute, bases cuneate (rarely rounded), lateral veins barely apparent on both surfaces, yellowish to pink; petioles (7.7-)11.3–17.5(-20.7) mm long; inflorescences cymes, sparse, terminal or axillary; flowers light pink turning deep pink with maturity (rarely with white interiors); floral-tube campanulate to cylindrical (2.6-)3.3–5.9(-7.0) mm long × (2.2-)2.4–3.4(-4.3) mm wide, with vertical keel below each corolla lobe; pedicels (0.5-)1.0–2.0 mm long; corolla lobes 4 (rarely 5), concave with thickened margins, papillate, (2.8-)2.6–4.2(-5.8) mm long × (1.6-)2.2–2.9(-3.0) mm wide; disk lobes lingulate, apices acute or round; stigma lobes 3; stamens 4, hairs proximal to the filaments (rarely hairs distal); ovary partly inferior (approx. ⅔); drupe elliptic, with subapical ring, 9–14 mm long; seed muricate, with pointed beak on one end.

Representative Specimens Examined—U. S. A. Hawaiian Islands: O‘ahu, Koolau Mts, Honolulu Watershed Forest Reserve, Lammers and Imada 5537 (MAK);Manana Ridge Trail, Harbaugh 318*, 322*, 323*, 324* (US); Aiea Loop Trail, Lee s. n. (BISH); Honolulu, Mauumae Ridge, Lanipo Trail, Lennstrom 1994–92 (BISH); Wai‘anae Mts., Honouliuli Preserve, Palehua Rd., Harbaugh 24*, 25*, 30* (UC); Wai‘anae Mts., West Makaleha Valley, along Ka‘ala Rd., Harbaugh 208*, 209*, 212*, 215*, 216* (US); Wai‘anae Mts., Honouliuli Preserve, Harbaugh 228*, 232*, 261*, 266*, 281* (US);

Common Names—Santalum freycinetianum is known as sandalwood, forest sandalwood, or Freycinet sandalwood (Pratt 1998), and by its Hawaiian name ‘iliahi (Kepler 1998).

Range and Environment—Santalum freycinetianum occurs scattered throughout the Wai‘anae and Ko‘olau Mountains on the island of O‘ahu from approximately 300–800 m in elevation. It grows in partial shade to full sun, and is often associated with native taxa such as Acacia koa and Metrosideros polymorpha, and nonnative Eucalyptus spp., Psidium cattleianum, and Schinus terebinthifolius (Oppenheimer, pers. obs.).

Conservation Status—With Moloka‘i populations now considered S. haleakalae var. lanaiense, this species is restricted to O‘ahu in both the Wai‘anae and Ko‘olau Mts. There are likely fewer than 1,000 plants (Oppenheimer, unpubl. data), so listing as a threatened species may be warranted.

Notes—Stemmermann (1980a) was the first to treat certain populations from the island of Moloka‘i as S. freycinetianum based on a few specimens. However, she said that “with further collections of plants from Moloka‘i it may be possible to recognize the Moloka‘i plants as distinct from S. freycinetianum at the varietal level, but that should only be done when the range of variation is better understood.” Wagner et al. (1999b) agreed with Stemmermann (1980a) that the plants on Moloka‘i should be considered S. freycinetianum, but that they are intermediate in morphology towards var. lanaiense (on Maui). The new evidence gathered in this study reveal that the Moloka‘i plants do not interbreed with plants of S. freycinetianum from O‘ahu (consistent with the geological history of the islands at the time of colonization to the islands) and are in fact genetically and morphologically indistinguishable from populations of S. haleakalae var. lanaiense from West and East Maui, and Lana‘i. Although the extremes of morphological variation are not present in Moloka‘i plants (namely plants with flat, wide leaves), the morphological characteristics fall within the great morphological diversity present within populations of S. haleakalae var. lanaiense on West and East Maui, and Lana‘i, and not within those from O‘ahu.

SANTALUM HALEAKALAE Hillebr., Fl. Hawaiian Isl: 390. 1888.—TYPE: U. S. A. Hawaiian Islands: Maui, Haleakala, 2440–3050 m, May 1872, W. Hillebrand & J. M. Lydgate s. n.* (holotype: B, presumably destroyed; lectotype, here designated: BISH-581851!; isolectotype: K!).

Tree, or shrubby tree, evergreen, single or multiple stems; leaves opposite, more glaucous abaxially, surface paler abaxially, apices acute or obtuse (rarely acuminate), bases cuneate, margins flat to slightly recurved; inflorescences cymes; flowers deep pink to red throughout, or with white to pink interiors; floral-tubes campanulate to cylindrical, without vertical keel below each corolla lobe; disk lobes lingulate, apices acute or round; corolla lobes 4 (rarely 5), concave with thickened margins, papillate; stigma lobes 3; stamens 4, hairs proximal to the filaments (rarely hairs distal); ovary partly inferior (approx. ⅔); drupe elliptic, with subapical ring; seed muricate, with pointed beak on one end. var. HALEAKALAE

Usually 1–8 m in height; leaves medium, olive to dark green, thickly coriaceous, broadly ovate, elliptic, to orbicular, (2.2-)2.9–5.1(-6.5) cm long × (1.2-)1.8–3.1(-4.0) cm wide; leaf lateral veins apparent on abaxial surface (to not apparent in thick leaves), yellowish to green; petioles (1.2-)2.0–7.4(-11.6) mm long; inflorescences dense to dense, terminal (rarely axillary); bracts 5 mm long, persistent; floral-tubes (2.0-)3.9–8.5(-10.0) mm long × (2.0-)2.2–3.4(-3.5) mm wide, pedicels (0.7-)1.0–3.2(-4.4) mm long; corolla lobes (2.7-)3.1–5.7-(7.1) mm long × (1.9-)2.1–3.3(-4.0) mm wide; drupe 9–14 mm long.

Representative Specimens Examined—U. S. A. Hawaiian Islands, Maui, Mann and Brighnam 396 (G); Koolau Gap, Degener 2277 (G); Haleakala Crater, Namanaokeakua, Stemmermann 749 (BISH); Haleakala National Park, Harbaugh 42*, 43* (UC); Haleakala, Alexander and Kellogg 5290* (BISH); Haleakala National Park, Hosmer's Grove Campground, Harbaugh 334*, 340*, 341*, 352*, 353* (US); Haleakala Ranch, Harbaugh 356*, 358* (US); Poli Poli/Kula Forest Reserve, Waiohuli Gulch, Harbaugh 359 (US); Kula Forest Reserve, Waiohuli, Oppenheimer H70709* (US, BISH); Kahikinui Forest Reserve between Pu‘ukeokeo and Kanahau, Oppenheimer and Perlman H110731* (US, BISH); Kahikinui Forest Reserve, SE of Pu‘ukeokeo, Oppenheimer and Perlman H110734* (US, BISH).

Common Names—Santalum haleakalae var. haleakalae is known as sandalwood or Haleakala sandalwood, and by its Hawaiian name ‘iliahi (Kepler 1998).

Range and Environment—Santalum haleakalae var. haleakalae is rare and is restricted to a single volcano, Haleakala on East Maui, and occurs at higher elevations (1,800–2,700 m) in subalpine and montane mesic forest plant communities.

Conservation Status—A large portion of the habitat of Santalum haleakalae var. haleakalae on the western slope has been converted to pasture and other agricultural uses. Seedlings are rarely, if ever, observed (Oppenheimer, pers. obs). Older trees readily spread vegetatively via root sprouts when surface roots are exposed or damaged, sometimes forming small stands. Threats include fire; browsing and/or trampling by introduced ungulates such as cattle (Bos taurus), goats (Capra hircus), deer (Axis axis), and pigs (Sus scrofa), and possibly black twig borer (Xylosandrus compactus). Seeds are commonly predated by rats (Rattus rattus, R. exulans), and mice (Mus domesticus). Competition for space, light, water, and nutrients with alien plant species such as Rubus argutus, R. niveus, Pinus spp., and Fraxinus uhdei are significant threats. Mat forming grasses such as Melinis minutiflora and Pennisetum clandestinum prevent seedling establishment (Oppenheimer, pers. obs.). Pollinators are mostly unknown but are probably depleted across the range. Dispersal is presumed by frugivorous passerines, many of which are also rare, endangered, or extinct. Additionally, there is at least one unconfirmed report of illegal harvesting of an unknown number of individuals in the past ten years. It is estimated that approximately 700 plants occur throughout its range, which is far more restricted than S. haleakalae var. lanaiense, which is currently listed on the USFWS Endangered Species List (as S. freycinetianum var. lanaiense). We suggest that further action should be taken to list S. haleakalae var. haleakalae as endangered.

Notes —We are transferring the formerly recognized S. freycinetianum var. lanaiense to a variety of S. haleakalae because there is no genetic evidence to separate it, and it is likely an ecological variant of the lower-elevation plants, which were considered a distinct species based on a variety of characters including its thick coriaceous leaves and bottle-shaped adaxial epidermal cells, congested cymes, deep red flowers, and persistent bracts. However, according to Wagner et al. (1999b) the “assignment to specific rank is tentative.” Additionally, Stemmermann (1980b) demonstrated that the development of the bottle-shaped adaxial epidermal cells characteristic of the highest elevation plants is correlated with environmental factors because there is a linear relationships between height of the cells and elevation. Leaf thickness and the density of the inflorescences appear also to be environmentally controlled, as there is a gradient with elevation and they intergrade with S. haleakalae var. lanaiense found at lower elevations on Haleakala.

var. lanaiense (Rock) Harbaugh, comb. nov. Santalum freycinetianum Gaudich. var. lanaiense Rock. Indig. trees Haw. Isl. 129 1913. Indig. Trees Haw. Isl.: 129. 1913. Santalum lanaiense (Rock) Rock, Hawai‘i Board Agric, and For., Bot. Bull. 3: 21. 1916.—TYPE: U. S. A. Hawaiian Islands: Lana‘i, on the highest ridge, Jul 1910, J. F. Rock 10061* (holotype: BISH-579847!).

Santalum freycinetianum Gaudich. var. auwahiense Stemmerm. Pacific Sci., 34(1): 47. 1980.—TYPE: U. S. A. Hawaiian Islands: Maui, Auwahi Forest Reserve, 1 Jun 1977, R. L. Stemmermann &. J. Kjargaard 2149* (holotype: BISH-430709!; isotypes: BISH-2 sheets!).

Usually 1–6 m in height; leaves light, olive, to dark green, chartaceous to coriaceous, narrowly to broadly ovate, to elliptic (rarely conduplicate-falcate), (3.4-)4.4–6.8(-8.4) cm long × (1.0-)1.6–3.1(-4.9) cm wide; leaf lateral veins apparent on both surfaces of the leaf, yellowish to dark purple; petioles (3.9-)7.4–15.4(-21.7) mm long; inflorescences fairly dense to dense, terminal or axillary; bracts 1–4 mm in length, not persistent; floral tubes (3.4-)4.2–8.0(-11.2) mm long × (1.9-)2.3–3.5 (-4.0) mm wide; pedicels (1.0-)1.5–2.9(-4.0) mm long; corolla lobes (2.0-)3.0–4.4(-4.8) mm long × (1.8-)1.9–2.7(-3.8) mm wide; drupe 10–16 mm long.

Additional Specimens Examined —U. S. A. Hawaiian Islands, Lana‘i, Kanepu‘u, St. John and Cowan 22625* (BISH); Kanepu‘u Forest, Munro 679* (BISH); Munro s. n* (BISH); Kanepu'u, Montgomery and Ruffin s. n. (BISH); Mt. near Koele, Forbes 114L (BISH); Forbes 327L (BISH); Mts. on east end, Forbes 229L (BISH); Head of Lopa Gulch, the short ridge just N of Puhielelu ridge, Lau 2868 (BISH); NW extremity of island, Stone 883 (BISH); W of divide, O. Degener 35806 (BISH); Munro Trail, open shrubby rainforest at the top, O. Degener 24257 (BISH); NW part of Munro Trail, O. Degener and Hobdy 24255 (BISH); Kanepu‘u, Desha et al. s. n. (BISH); Kaa, Kanepu‘u, Herbst and Spence 5789 (BISH); Kanepu‘u, Little 31251 (BISH); Kanepu‘u, Stemmermann 811, 812, 813 (BISH); Lanaihale peak in Metrosideros forest, Little 31233 (BISH); Munro 211, 951 (BISH); Gulches between Kehewai and Kahinahina, Perlman and Montgomery 6375 (BISH); Pu‘u A‘ali‘i, Kealia Aupu-Kaunolu divide, St. John and Fames 18712 (BISH); Kanepu‘u Preserve, Harbaugh 374*, 375*, 376* (US); headwaters of Wai‘opa Gulch, NE of Ha‘alelepa‘akai, Oppenheimer and Perlman H90704* (US, BISH); Puhielelu Ridge, near exclosure fence, Oppenheimer and Perlman H100732* (US, BISH). West Maui, Lahaina District, on a ridge dividing Kahoma Valley and Kealii Gulch, Oppenheimer et al. H20011 (BISH); Mts. above Napili and pineapple plantations, watershed land, Smith 2900* (UC); lowland ohia mixed forest, Welton and Haus 1507 (BISH); Hanaula, Ukumehame District, head of Papalaua Gulch, Medeiros 540 (BISH); Pu‘u Kukui Watershed Preserve, Transect 4, Harbaugh 360*, 364*, 366*, 367*, 369* (US); South of Ukumehame, gulch of Hana‘ula Iki, Oppenheimer H60722*, H60723* (US, BISH); Ridge NE of Kaua‘ula Valley, Kaua‘ula/Manowaiopae Divide, Oppenheimer et al. H100707*, H100708* (US, BISH); Wailuku District, Pohakea Gulch, Oppenheimer and Baldwin H110730* (US, BISH); Oppenheimer and Perlman H100701* (US, BISH). East Maui, Auwahi 8 mi E of Ulupalakua, S slope of Haleakala Crater, Little 31131* (BISH); Auwahi District, S slope of E Maui, Medeiros 196 (BISH); Auwahi, St. John 26863 (BISH); Auwahi SE Puu Ouli, S slope of Haleakala, Fosberg 41515a (BISH); Auwahi land beyond Ulupalakua, Sohmer 6603 (BISH); Haleakala S slope, just above the pipeline Rd. on W side of Auahi-Kanaio border, Medeiros 182 (BISH); Auwahi Forest Reserve, Stemmermann and Hobdy 755 (BISH); E. Funk's Geranium arboreum study site at Polipoli, Takeuchi and Funk East Maui 7a (BISH); Koolau Gap on N. slope of Haleakala, Stemmermann 734 (BISH); Auwahi Preserve, in Ulupalakua Ranch, along 4WD road, Harbaugh 394*, 395*, 396*, 406*, 413* (US). Moloka‘i, Russell s.n.* (BISH); Kikiakala on steep gulch slope N of Kamiloloa, Hobdy 1163* (BISH); Lands of Makakupaia, Makakupaia Ridge jeep trail, Wagner et al. 4933 (BISH); Kawela AHU, Pu‘u Hoi Ridge; upper part of Pelekunu Valley on narrow ridge, Warshauer and McEldowney 3003 (BISH); Wawa‘ia AHU, Tr 9 (15); ridge E of Kua Gulch, Stemmermann and Montgomery 3896 (BISH); Kawela AHU, Tr 5 (19); Along W form of Kawela Gulch, Warshauer and McEldowney 2332 (BISH); ridge between east forks of Kawela Gulch, Davis 790 (BISH); upper Kaunakakai Pl along Makakupaia Rd., Hobdy 2619 (BISH); Kamakou reserve E. side of Kawela ridge, due SW of Puu O Kaeha, Lorence et al. 5612 (BISH); Puu Hoi rdige, Pelekunu valley, Kepler s. n. (BISH); upper Kaunakakai along Makakupaia, Hobdy 2620 (BISH); Kamakou Preserve, Harbaugh 384*, 386*, 388*, 389*, 393* (US); Kikiakala, Headwaters of Waihanau Stream, Oppenheimer H10811* (US, BISH); Central west fork of Kawela Gulch, Oppenheimer and Perlman H40815* (US, BISH); W side of Waiakuilani Gulch, east of Pu‘u Kolekole, Oppenheimer and Perlman H80706* (US, BISH).

Common Names—Santalum haleakalae var. lanaiense is known as sandalwood, or Lana‘i sandalwood, and by its Hawaiian name ‘iliahi (Kepler 1998).

Range and Environment—Scattered and rare in exposed or semishaded scrublands in the West Maui mountains (from 800–1,300 m), scattered on the southern slope of Haleakala Crater on East Maui (1,200–1,350 m), rare within the Kanepu‘u Preserve on western Lana‘i (550 m), scattered in the mountains of eastern Lana‘i (750–950 m), and scattered in upper elevations of eastern Moloka‘i (950–1,250 m). It is often associated with the following plant groups: Metrosideros, Sadleria, Nephrolepis, Canavalia, Vaccinium, Alyxia, Myrsine, Clermontia, Dubautia, Doodia, Liparis, Dodonaea, Wikstroemia, Leptecophylla, Coprosma, Myoporum, Diospyros, Pisonia, Melicope, Pittosporum, Dryopteris, and Bidens.

Conservation Status—Listed as Endangered by the US Fish & Wildlife Service (Herbst 1986), Santalum haleakalae var. lanaiense is now considered to occur on three islands. Despite this distribution, seedlings are rarely, if ever, observed. It spreads locally via vegetative means by root sprouts when surface roots are damaged or exposed. Threats include fire; and browsing and/or trampling by introduced ungulates such as goats (Capra hircus), deer (Axis axis), mouflon sheep (Ovis musimon), and pigs (Sus serofa). Seeds are commonly predated by rats (Rattus rattus, R. exulans), and mice (Mus domesticus). Competition for space, light, water, and nutrients with alien plant species such as Clidemia hirta, Grevillea robusta, Leptospermum scoparium, Morella faya, Psidium cattleianum, Acacia melanoxylon, Fraxinus uhdei, Tibouchina herbacea, Rubus argutus, R. discolor, and Schinus terebinthifolius also degrades habitat. Mat forming grasses such as Melinis minutiflora prevent seedling establishment. The black twig borer (Xylosandrus compactus) potentially attacks these trees, and herbivory by several introduced slugs commonly found across its range likely prevents reproduction. Pollinators are mostly unknown but are probably depleted across the range. Dispersal is presumed by frugivorous passerines, many of which are also rare, endangered, or extinct. Fewer than 2000 plants are believed to occur (Oppenheimer, unpubl. data).

Notes —No genetic evidence was gathered to support separating populations of S. haleakalae var. lanaiense from Maui, Moloka‘i, and Lana‘i into separate varieties. This is a morphologically variable taxon, with leaf shapes, textures, and sizes ranging greatly, even within a population. However, several morphological characters unite these populations, including a paler abaxial side of the leaves, often dark purplish lateral veins in younger leaves, and deep red flowers at maturity, often with white interiors in younger flowers. With limited data, Stemmermann (1980a) observed that the Moloka‘i plants were intermediate between those found on O‘ahu and Lana‘i, but assigned them to S. freycinetianum; with no new data to say otherwise, Wagner et al. (1999b) chose to retain the circumscription of Stemmermann (1980a). However, upon the inspection of a wide range of specimens, it is clear that these plants fall within the ranges of morphological diversity of populations of S. haleakalae var. lanaiense from Lana‘i and Maui, which is consistent with results of the genetic analyses.

SANTALUM INVOLUTUM H. St. John, Phytologia, 55(4): 220. 1984.—TYPE: U. S. A. Hawaiian Islands: Kaua‘i, between Ke‘e and Hanakapiai, ridge top on NE side of last stream NE of Hanakapiai, 25 Jul 1976, C. Christensen 38* (holotype: BISH-498267!; isotypes: BISH-3 sheets!).

Small tree, evergreen, usually 2–7 m in height; leaves opposite, yellowish-green to grayish-green, chartaceous (often translucent), often drooping, more glaucous and slightly lighter on abaxial surface, linear elliptic (rarely conduplicatefalcate), sides involute (rarely flat), (4.6-)5.7–8.1(-8.2) cm long × (1.4-)1.5–1.7(-1.8) cm wide, margins flat, apices acute, bases cuneate, lateral veins slightly apparent on adaxial surface; midvein yellowish, petioles yellowish to pinkish, (7.0-)8.1–16.3(-17.0) mm long; inflorescences cymes, sparse terminal or axillary; flowers greenish-white throughout (sometimes turning red with age); floral tubes campanulate to cylindrical, (5-)6–9(-11) mm long × 2–3 mm wide, without vertical keel below each corolla lobe; corolla lobes 4, concave with thickened margins, 3–4(-5) mm long × 1.5–3 mm wide; disk lobes lingulate, apices acute or round; stigma lobes 3; stamens 4; ovary inferior; drupe elliptic, with apical ring, 13–20 mm long; seed muricate, with pointed beak on one end.

Representative Specimens Examined —U. S. A. Hawaiian Islands, Kaua‘i, Kalalau Valley, N side and E of Keanapuka Falls, (2,450 ft.), Wood and Holmes 12482* (PTBG); Hanalei District, Pohakuao, hanging valley between Kalalau and Hanakoa (600 m), Wood et al. 1770* (PTBG); Wainiha Valley, Wainiha (400 ft), Fosberg and Sachet 13946* (BISH); west of Waioli-Waipa Ridge in Koa forest (1,100 ft), Christensen 69* (BISH); Lumahai-Wainiha Ridge, sides of ridge (1,000 ft), Christensen 182* (BISH); Wahiawa, edge of Kanaele Bog (2,100 ft), St. John 26766* (BISH); Wainiha Valley 1 1/8 mile in from last house (650 ft), Christensen 121* (BISH); Na Pali Coast, Hanakapiai Ridge E. of stream (800–1,200 ft), Christensen 57* (BISH).

Common Names —Santalum involutum has not been commonly recognized, though it would be considered by its Hawaiian name ‘iliahi. However, based on its Latin name and characteristic leaf margins, we suggest that this species be known as involute sandalwood.

Range and Environment —Santalum involutum is restricted to Kaua‘i and occurs in the northwestern Na Pali coast valleys of Hanakapiai, Pohakuao, and Kalalau, in addition to the northern valley of Wainiha and the southern region of Wahiawa (120–750 m). Although observed in Metrosideros wet forest, this species seems to prefer Diospyros mixed mesic forest which is extremely rare and known for its floristic diversity. Some of the associated genera, many of which are represented by numerous species, include Acacia, Alphitonia, Bobea, Euphorbia, Charpentiera, Coprosma, Cyanea, Cyrtandra, Diospyros, Dodonaea, Dubautia, Elaeocarpus, Eugenia, Exocarpos, Flueggea, Hibiscus, Ilex, Isodendrion, Kadua, Kokia, Labordia, Lysimachia, Melicope, Metrosideros, Myrsine, Neraudia, Nesoluma, Nestegis, Nototrichium, Pipturus, Pisonia, Pittosporum, Platydesma, Pleomele, Pouteria, Psychotria, Pteralyxia, Rauvolfia, Schiedea, Tetraplasandra, Wilkesia, Xylosma, and Zanthoxylum.

Conservation Status —Santalum involutum is in need of further field research to better understand its distribution and abundance. Plants have not been observed around the holotype locality for more than 30 yr, and at this time it is only known from isolated forest pockets in Pohakuao and Kalalau valleys. Currently S. involutum should be considered endangered considering its small range and area of occupancy, in addition to its low numbers (ca. 50–100 trees; Wood unpubl. data). This taxon is threatened by fire, loss of habitat, limited gene pool, and invasive nonnative species similar to those that threaten S. pyrularium.

Notes —The results from this study indicate that S. involutum is an ancient hybrid based on molecular data and this is consistent with morphological characters: the leaf-shape, floral tube shape, and overall habit have aligned it with the red-flowered taxa, although morphological characters first observed by St. John (1984) as distinguishing it from S. pyrularium, namely its shorter campanulate, white to greenish flowers, as well as inferior ovary and apical drupe ring unite S. involutum with the S. ellipticum clade (Harbaugh 2007). The exclusion of these plants from S. pyrularium helps to more clearly define S. pyrularium as a unique species. Stemmermann (1980a) had dropped S. freycinetianum var. pyrularium from specific rank in part because of the significant variation in floral tube length, and in the rugosity of the endocarp (Skottsberg 1944); however this may be explained by the consideration of plants now separated into two distinct species, S. pyrularium and S. involutum.

The discovery of a distinct lineage of ancient hybrid origin between the two Hawiian Santalum clades, in the rugged coastal valleys on northwestern Kaua‘i is not surprising given that it is home to a great diversity of other restricted endemics, including species of Schieden (Wagner et al. 1994), Dubautia (Baldwin and Carr 2005), Remya (Wagner and Herbst 1987), Hibiscadelphus (Lorence and Wagner 1995), Chamaesyce (Lorence and Wagner 1996), Stenogyne (Wagner and Weller 1991), Nototrichium (Lorence 1996), Tetraplasandra (Lowry and Wood 2000), and Kadua (Wagner and Lorence 1998), many of which are rare and endangered (Wood and Perlman 1993; Wagner et al. 1999a).

SANTALUM PYRULARIUM A. Gray, Proc. Amer. Acad. Arts 4: 327. 1860. Santalum freycinetianum Gaudich. var. pyrularium (A. Gray) Stemmerm., Pacific Sci., 34(1): 48. 1980.–TYPE: U. S. A. Hawaiian Islands: Kaua‘i, 1838–42, US Exploring Expedition s. n. (holotype: US-00055059!; isotype: P!).

Santalum majus H. St. John, Phytologia, 55(4): 223. 1984.-TYPE: U. S. A. Hawaiian Islands: Kaua‘i, Kumuela Ditch Trail, along border between Koke‘e State Park and Na Pali-Kona Forest Reserve, 13 Aug 1964, M. R. Crosby & S. Anderson 2024* (holotype: BISH-68301!).

Santalum pyrularium A. Gray var. sphaerolithos Skottsb., Vascular plants from the Hawaiian Islands. 4:359.1944.—TYPE: U. S. A. HAWAIIAN ISLANDS.: Kaua‘i, Alakai, 16 Aug 1938, L. M. Cranwell & C. Skottsberg 2979* (holotype: BISH-579831!).

Small tree, or shrubby tree, evergreen, usually 1–5 m in height, with a single or multiple stems; leaves opposite, medium to dark green, chartaceous to coriaceous, more glaucous abaxially, surface not much paler on abaxial surface, narrowly to broadly elliptic, ovate, to oblong (rarely conduplicate-falcate), (3.6-)5.4–7.8(-9.4) cm long × (1.2-)2.1–3.2 (-3.8) cm wide, margins flat (rarely wavy), apices acute to obtuse (rarely acuminate), bases cuneate or rounded, lateral veins apparent on both surfaces of the leaf, yellowish to bright purple; petioles (5.9-)7.8–12.6(-15.7) mm long; inflorescences cymes, sparse, axillary (rarely terminal); bracts 1–4 mm, not persistent; flowers cream to purple throughout, or greenish with purple interior; floral-tubes campanulate to cylindrical, 3.6–8.5(-13.0) mm long × (2.6-)2.9–4.3(-4.4) mm wide, with vertical keel below each corolla lobe; pedicels (1.0-)1.1–2.7 (-3.1) mm long; corolla lobes 4, concave with thickened margins, papillate, (3.4-)4.2–5.6(-5.8) mm long × (2.0-)2.4–3.3 (-3.7) mm wide; disk lobes lingulate, apices acute or round; stigma lobes 3; stamens 4, hairs proximal to the filaments (rarely hairs distal); ovary partly inferior (approx. ⅔); drupe elliptic, with subapical ring, 15–22 mm long; seed muricate, with pointed beak on one end.

Representative Specimens Examined —U. S. A. Hawaiian Islands, Kaua‘i, Koloa District, Lihue-Koloa Forest Reserve, Wahiawa Bog, hammers et al. 5863 (BISH); Wahiawa Bog, Herbst 2230 (PTBG); Waimea District, Na Pali-Kona Forest Reserve, Lorence 5218* (BISH); Waimea Canyon State Park, Hwy 550 near mi 11.5, Lorence and Jamieson s. n. (BISH); Waimea Canyon/Koke‘e State Park, on Hwy 550, Harbaugh 02*, 05* (UC); Waimea Canyon State Park, Hwy 550 near mile 11.5, Flynn 2744* (BISH); Koke‘e State Park, along the Awaawapuhi trail, Harbaugh 415*, 425*, 426*, 430*, 431* (US); Alakai Picnic area, Harbaugh 438*, 441*, 447*, 451* (US); Na Pali-Kona Forest Reserve, Harbaugh 456*, 459*, 460*, 461*, 463*, 471* (US); Waimea Canyon, along Hale ele ele Ridge Road, Regalado 671 (PTBG); Hwy. 55 near entrance to Kokee State Park, Spence 191 (PTBG); Poomau Canyon Lookout Trail, Flynn 139 (PTBG); upper Kawaiiki, Kaluahaulu Ridge (Mohihi-Waialae Trail), Wood 764 (PTBG); Honapu Trail, Darwin 1127 (PTBG); Waimea district, Na-Pali Kona Forest Reserve, Makaha Valley, Lorence et al. 5218 (PTBG); Near Kalahu, Kalalau Valley, Degener and Hathaway 21369* (BISH); Kalalau Valley, slopes of Kalahu, 300 m east of navy plane crash (2,500 ft), Wood and Perlman 3393* (PTBG); upper Honopu drainage (north side), (3,550–3,700 ft) Wood 4923* (PTBG); Kalalau, lower Kalahu side w/ rope, Wood 3647* (2,000 ft) (PTBG); Kalalau Rim, Kalahu side between and west of first lookout, 300 m east of plane crash (700–800 m), Wood 1414* (PTBG); Haena-Kalalau Trail, in Hoolulu Valley, Na Pali Kona Coast, Carlquist 1645 (BISH); ridge between Kalahu and Nianiau, between Kalalau and Honapu Valleys, Fosberg 12129 (BISH); Kalahu Trail, below Kalalau Lookout (3,700 ft), Stone 1618 (BISH); N. side of Awaawapuhi Stream, Christensen 183 (BISH).

Common Names—Santalum pyrularium is known commonly as sandalwood, or by its Hawaiian name ‘iliahi (Kepler 1998).

Range and Environment —Santalum pyrularium is restricted to Kaua‘i (270–1,400 m) and can be common around Waimea Canyon and Koke‘e State Parks where it consistently prefers partial to full shade. It is most often associated with mesic (summer dry) forest communities growing with genera such as Acacia, Alphitonia, Coprosma, Diospyros, Ilex, Kadua, Melicope, Metrosideros, Myrsine, Nestegis, Pittosporum, Pleomele, Pouteria, Psychotria, Tetraplasandra, and Xylosma. It occasionally penetrates wet forest communities and bog margins where it is associated with genera such as Metrosideros, Cheirodendron, and Dicranopteris.

Conservation Status —Santalum pyrularium can occasionally be a codominant in mesic forest communities and is not considered rare (ca. 10,000 + trees; Wood, unpubl. data). Never the less, this taxon is threatened by fire, loss of habitat, and invasive nonnative species. Nonnative animals include goats (Capra hircus), black-tailed deer (Odocoileus hemionus), pigs (Sus serofa), rats (Rattus spp.), and mice (Mus domesticus). Some of the more threatening nonnative plant taxa include Psidium guajava, P. cattleianum, Lantana camara, Rubus argutus, Hedychium gardnerianum, Clidemia hirta, and Melinus minutiflora.

Notes —In 1927 Skottsberg recognized S. pyrularium as distinct from S. freycinetianum based on its long and narrow disc lobes and large fruit: the receptacle is wider in S. pyrularium and of nearly the same width across the rim as the base, and the drupe is much larger and rugose in S. pyrularium. Stemmermann (1980a) reduced S. pyrularium to a variety of S. freycinetianum because some collections had flowers 7 mm long (including pedicel), which is shorter than the recorded measurements for the flowers of this taxon and falls into the range of flower length for S. freycinetianum. The variability in these characters may be accounted for by the inclusion of individuals in Stemmermann's analysis from both S. pyrularium and S. involutum, as S. involutum tends to have flowers that are much shorter than S. pyrularium. Interestingly, a specimen annotated by H. St. John himself as S. involutum (Degener and Hathaway 21369) fits well within the morphological variability of S. pyrularium, as it has long dark-colored flowered, coriaceous elliptical leaves, and short petioles.