A new species, Phyllanthus mutisianus, is described on the basis of a collection from Colombia made by the expedition of José Mutis. It is distinguishable from all other neotropical species of Phyllanthus by virtue of the distinctive leaf venation and very long fruiting pedicels. The type specimen lacks mature flowers, but the vegetative morphology, inflorescence, and fruiting structures suggest placement in subgenus Xylophylla, section Elutanthos.
According to the recent compilation of Govaerts et al. (2000), Phyllanthus is the third largest genus in the Euphorbiaceae, with over 800 species. About one forth of the species are confined to the neotropics, but many remain poorly known. The only comprehensive revisions of the American species since that of Müller Argoviensis (1866, 1873) are those of the West Indian species by Webster (1956–58) and the species of the Guayana Highlands by Jablonski (1967). During my study of the neotropical species during the past four decades, a number of new taxa have been described (Webster, 1966, 1967; Webster and Proctor, 1984; Webster and Huft, 1988), and additional species and supraspecific taxa have been delineated (Webster, ined.).
One of the most remarkable species encountered during this protracted study of the neotropical species of Phyllanthus is a specimen from the U. S. National Herbarium collected in Colombia by members of the expedition headed by José Mutis (Fig. 1). It consists of two twigs that have the appearance of deciduous branchlets, one with two fruiting pedicels. The large caudate-acuminate leaves are unusual in that the proximal three of the four or five .major laterals are concentrated in the lower half of the blade. Even more striking are the remarkably long (16–17 cm) and slender fruiting pedicels, these are among the most elongated in any neotropical Phyllanthus, being matched only by the Brazilian P. cladotrichus Mull. Arg. (synonymized with P. ramosus Veil, by Govaerts et al., 2000).
Because of the lack of mature flowers, it is challenging to determine the affinities of this very striking species,. The flowers are produced on axillary bisexual inflorescences with a terminal (central) pistillate flower and paired lateral repeatedly branched staminate dichasia (Fig. 2). Unfortunately, the staminate inflorescences bear only very immature flowers (attempts to extract pollen were unsuccessful), and the pistillate flowers are represented only by the fruiting pedicel, persistent sepals, columella, and fragments of immature fruits. The repeatedly branched staminate dichasium is unusual in contrast to the glomerular or thyrsoid disposition in most species of Phyllanthus. However, some species of sect. Elutanthos Croizat, such as P. grandifolius L., have thyrsoid infloresences in which the ultimate units (Fig. 3) resemble the inflorescence of the Colombian plant. This resemblance strongly suggests a possible relationship, and it appears that P. mutisianus may prove to be a very aberrant species of sect. Elutanthos.
A search was made to identify other possible candidate genera for the new species among neotropical taxa of subfamilyPhyllanthoideae. The elongated slender fruiting pedicels suggest a possible affinity with Meineckia, but the seeds in the Mutis specimen, although immature, have a smooth testa very different from the arcuate seeds with foveolate testa found in Meineckia. Furthermore, in all species of Meineckia the staminate flowers are borne in condensed glomerules quite unlike the branching dichasia of the Mutis plant.
Type: COLOMBIA: without locality, Mutis 1902 (Holotype: US 1561418!; Isotype, MA).
Ab aliis speciebus sect. Elutanthos differt pedicellis ♀ longissimis, foliis magnis cuspidato-acuminatis; a P. cladotricho differt floribus ♀ solitariis, floribus ♂ in dichasiis pedunculatis.
Glabrous shrub or tree; branchlets terete, somewhat angled, 19–25 cm long × 2 mm thick, with c. 5 leaves; leaf blades chartaceous, elliptic, 12–25 cm long, 5–9.5 cm broad, caudate-acuminate (acumen 3–4 cm long), with 3 main vein pairs (of the 4 or 5) arching from proximal half; midrib slightly sunken adaxially, midrib and laterals strongly raised abaxially, veinlets prominulous; petioles 4–5 mm long; stipules scarious, entire, lanceolate, 4–7 mm long, 2–2.5 mm broad. Flowers axillary, in bisexual or staminate cymes, the pistillate flower solitary, the staminate several on branches of a pedunculate dichasium 6–8 mm long with slender axes (0.1–0.2 mm thick). Staminate flowers [observed only in bud]: pedicel 2–3 mm long, sepals 4, elliptic, c. 0.7 mm long; disk apparently of 4 segments; stamens 2, filaments free, anthers dehiscing longitudinally. Pistillate flowers [observed only in fruit]: pedicel terete, smooth, 16–17 cm long, c. 0.5 mm thick; sepals 5 (?), c. 2.5 mm long; disk patelliform. Fruits seen only as thin-walled valves 10–11 mm long; columella 4 mm long × 1.5 mm thick; seeds [immature] trigonous, smooth, pale brown, c. 5.5–6 mm long.
Distribution and habitat: The species is known only from the type collection, which lacks data except for the indication that it is from Colombia. In the enumeration of Mutis specimens of Blanco y Fernandez de Caleya (1991), Mutis 1902 is not listed, but localities of Mutis collections overall are summarized (in addition to the Bogotá area) as including Tolima (cabecera Mariquita) and Chocó, as well as collections in Ecuador by Caldas.
It is highly appropriate to name this striking plant in honor of the celebrated “father of Colombian botany,” Jose Mutis y Bosio (1782–1806). Despite its very unusual features, Phyllanthus mutisianus may be tentatively referred to subgenus Xylophylla on the basis of its resemblances to species of sect. Elutanthos. In the unpublished revision of the neotropical species of Phyllanthus (Webster, ined.), it does not easily fit into any section. More complete material is required to determine whether it can be accomodated within sect. Elutanthos, or should be assigned to a new section.
I wish to thank the staff of the United States National Herbarium (US) for their patience in awaiting identification of the Mutis specimen. Dr. José Cardiel, of the Real Jardín Botánico (Madrid) provided information about the Mutis collections. Ellen Dean, Director of the University of California at Davis Herbarium, generously provided space and facilities for my studies. The photographs were taken by Sam Woo and Earl Schellhous at the Instructional Technology and Digital Media Center at the University of California, Davis.