Rubiaceae is one of the five largest families of flowering plants with over 13,000 species. We have seen a tremendous increase in our understanding of the phylogeny of the family through studies on molecular data during the 15-year period from 1991 to 2005; some new relationships are completely unexpected and different from traditional classification. At the end of 2005, ca. 50 phylogenetic reconstructions from the family had been published based on more than 4400 sequences. Most studies are based on ITS and rbcL sequences, but 13 different markers have been used. Most sequences available in GenBank (as of 2005) are from rps16, trn(T)L-F, rbcL, and ITS. We can now see a framework of the family phylogeny with support for three subfamilies and over 43 tribes; subfamily Cinchonoideae (Chiococceae, Cinchoneae, Guettardeae, Hamelieae, Hillieae, Hymenodictyeae, Isertieae, Naucleeae, Rondeletieae), subfamily Ixoroideae (Alberteae, Bertiereae, Coffeeae, Condamineeae, Cremasporeae, Gardenieae, Ixoreae, Mussaendeae, Octotropideae, Pavetteae, Posoquerieae, Retiniphylleae, Sabiceeae, Sipaneeae, Vanguerieae), and subfamily Rubioideae (Anthospermeae, Argostemmateae, Coussareeae, Craterispermeae, Danaideae, Gaertnereae, Knoxieae, Lasiantheae, Morindeae, Ophiorrhizeae, Paederieae, Psychotrieae, Putorieae, Rubieae, Schradereae, Spermacoceae, Theligoneae, Urophylleae), and tribe Coptosapelteae, which is placed outside the three subfamilies. Two of these tribes, Gardenieae and Morindeae, are paraphyletic/polyphyletic. Only about half of the tribes have been the focus of specific investigations. However, we have seen increased interest in using Rubiaceae phylogenies for studies of ecology, evolution, and biogeography, e.g., and also for morphological and anatomical investigations. Evolution of fruit traits, flower types, and myrmecophytism has been investigated, and biogeographic patterns for specific taxa in Africa, the Caribbean, and the Pacific have been studied. In addition, distribution of pollen types, chemical substances, and wood characteristics have been compared with molecular phylogenies.

Galianthe subg. Galianthe Griseb. se caracteriza por el fruto de mericarpios dehiscentes, semillas rollizas o complanadas con bordes aliformes, inflorescencias generalmente amplias tirsoides o pleiotirsoides, flores heterostilas, hábito erecto generalmente con xilopodio y cromosomas x = 8. Está representada por 39 especies sudaméricanas que se agrupan en dos secciones: sect. Galianthe (30 especies) y una nueva sect. Laxae E. L. Cabral (nueve especies y dos subespecies). Se acompañan claves para diferenciar las secciones y las especies de cada sección, con resumen sinóptico de las especies y mapas de distribución. Se designan neotipos para cuatro nombres: Borreria angustifolia Cham. & Schltdl. [= G. angustifolia (Cham. & Schltdl.) E. L. Cabral], B. equisetoides Cham. & Schltdl. [= G. equisetoides (Cham. & Schltdl.) E. L. Cabral], B. thalictroides K. Schum. [= G. thalictroides (K. Schum.) E. L. Cabral], B. valerianoides Cham. & Schltdl. [= G. valerianoides (Cham. & Schltdl.) E. L. Cabral]. Se designan lectotipos para cinco nombres: B. centranthoides f. glabrior Chodat & Hassl. [= G. centranthoides (Cham. & Schltdl.) E. L. Cabral], B. ericoides Cham. & Schltdl. [= Galianthe peruviana (Pers.) E. L. Cabral], B. leiophylla K. Schum. [= G. fastigiata Griseb.], G. hassleriana (Chodat) E. L. Cabral y G. verbenoides (Cham. & Schltdl.) Griseb.

The tribe Retiniphylleae and its single genus Retiniphyllum Bonpl. contains 22 species of shrubs and small trees that grow in white sand soils mostly in the Guayana Region of South America. The circumscription of the tribe is based on the diagnostic characteristic of two collateral and pendulous ovules per locule, a rare condition in the Rubiaceae. However, for the same reason, its placement within the family has been controversial. The monophyly and systematic position of the tribe Retiniphylleae and Retiniphyllum were tested based on a phylogenetic analysis of trnL-F and rps16 sequence data. The results confirm the monophyly of the tribe and genus Retiniphyllum. The tribe is placed sister to the core members of the subfamily Ixoroideae s. str. The genera Botryarrhena Ducke and Scyphiphora C. F. Gaertn. are not related to the tribe Retiniphylleae, as formerly hypothesized.

Analyses of distribution, diversity, endemism, and taxonomic effort for Rubiaceae are reported, based on queries from a World Rubiaceae Checklist database. Rubiaceae are widespread and occur in all major regions of the world except the Antarctic Continent, but are predominantly a group in the tropics with greatest diversity in low- to mid-altitude humid forests. A count of Rubiaceae species and genera is given (13,143 spp./611 genera), which confirms that this is the fourth largest angiosperm family. Psychotria L. is the largest genus in the Rubiaceae (1834 spp.) and the third largest angiosperm genus. Most genera (72%) have fewer than 10 species and 211 are monotypic. Calculation of relative species diversity and percentage endemism enables areas of high diversity and endemism to be enumerated, and identifies areas where further field collecting and taxonomic research are required. Endemism is generally high in Rubiaceae, which supports data from recent studies showing that many species have restricted distributions. Given the assumed ecologic sensitivity of Rubiaceae, in combination with a range of other factors including restricted distribution, we suggest that species in this family are particularly vulnerable to extinction. The rate at which new species are being described is inadequate; more resources are required before the diversity of Rubiaceae is satisfactorily enumerated.

The tribe Posoquerieae was recently described to include the genera Posoqueria Aubl. and Molopanthera Turcz. based on floral morphology, palynology, the presence of the pollen catapult mechanism, and molecular phylogenetic evidence. The floral morphology of these two genera was first recognized as unique in the Rubiaceae by Schumann. Both genera have stamens initially united into an ellipsoidal structure held at an oblique position, with the ventral stamen that springs forward when touched, while the two lateral stamens fold outward. Since their descriptions were published, Posoqueria and Molopanthera have been positioned in several distantly related tribes within the Rubiaceae. The close relationship between the two genera was only recently revealed by molecular phylogenetic studies. The taxonomic history of Posoqueria and Molopanthera is reviewed, and a general morphological comparison (particularly of stamen morphology and pollen catapult mechanism, and observations about pollination biology) of both genera is presented here. The pollen catapult mechanism of Molopanthera is described here in detail for the first time and concluded to be practically identical to that of Posoqueria.

Fossils of 134 taxa attributed to the Rubiaceae are described or mentioned in 115 publications dating from 1850 and from deposits as old as the Cretaceous and Paleocene. Close scrutiny of these records indicates, however, that the oldest and most likely (accepted) representatives of the family are four genera, Emmenopterys Oliv. from the Middle Eocene of Oregon and Washington, U.S.A., Faramea Aubl. from the Late Eocene of Panama, and Guettarda L. (cf. as †Guettardidites; †= fossil taxon) and Canthium Lam. (as †Rubipollis oblatus) from the Late Eocene of Australia, and a probable fifth genus, the alternate-leaved †Paleorubiaceophyllum eocenicum from the Middle Eocene of Tennessee/Kentucky, U.S.A. The record represents three subfamilies (Rubioideae, Ixoroideae, Cinchonoideae) from three widely separated geographic regions, implying an earlier origin in the Late Cretaceous or Paleocene. From the Oligocene, there are six accepted genera, Coprosma J. R. Forst. & G. Forst., Coprosma–Opercularia, Faramea Aubl., Macrosphyra Hook. f. (as †Triporotetradites hoekeni), Mitragyna Korth. (as †Retitricolporites annulatus), and Pinckneya Michx. from Africa (Cameroon), Australia and New Zealand, U.S.A. (Oregon), and Puerto Rico. The period of greatest diversification and radiation was in the Miocene, with 20 accepted genera reported from North America, Central America, South America, Southeast Pacific–Asia, Africa, and Europe. Stages in the evolution of three characters are further suggested by the fossil record. The relatively uncommon occurrence of alternate leaves among modern taxa is typical of advanced genera (e.g., Didymochlamys Hook. f., Sabicea Aubl., Theligonum L.), but this feature may have already developed by the Middle Eocene (†Paleorubiaceophyllum). Polyploidy is suggested in the Middle Eocene P. eocenicum var. lawrensis by epidermal cells 32 µm in diameter or nearly twice the size of the other varieties. Pollen polymorphism, possibly coordinated with or as a prelude to heterostyly, is represented by the diporate pollen of Faramea in the Late Eocene, and triporate and tetraporate forms in the Miocene and Pliocene. Currently, the principal needs are: (1) to clarify pending Paleocene records of †Cinchonidium (Cinchona L.), North Dakota, U.S.A.; Galium L., Greenland; and †Psilatricolpites coprosmoides (Coprosma, Chile); and (2) to examine the several large Cretaceous megafossil floras now under study (e.g., Anfiteatro de Ticó, Argentina; Crato, Brazil; Turonian-age floras, New Jersey and Sweden) for specimens with features that suggest a rubiaceous complex or with an aggregation of features suggesting presence of the family.

In its current circumscription, the herbaceous tribe Spermacoceae s.l. (Rubiaceae, Rubioideae) unites the former tribes Spermacoceae s. str., Manettieae, and the Hedyotis–Oldenlandia group. Within Spermacoceae, and particularly within the Hedyotis–Oldenlandia group, the generic delimitations are problematic. Up until now, molecular studies have focused on specific taxonomic problems within the tribe. This study is the first to address phylogenetic relationships within Spermacoceae from a tribal perspective. Sequences of three plastid markers (atpB-rbcL, rps16, and trnL-trnF) were analyzed separately as well as combined using parsimony and Bayesian approaches. Our results support the expanded tribe Spermacoceae as monophyletic. The former tribe Spermacoceae s. str. forms a monophyletic clade nested within the Hedyotis–Oldenlandia group. Several genera formerly recognized within the Hedyotis–Oldenlandia group are supported as monophyletic (Amphiasma Bremek., Arcytophyllum Willd. ex Schult. & Schult. f., Dentella J. R. Forst. & G. Forst., Kadua Cham. & Schltdl., and Phylohydrax Puff), while others appear to be paraphyletic (e.g., Agathisanthemum Klotzsch), biphyletic (Kohautia Cham. & Schltdl.), or polyphyletic (Hedyotis L. and Oldenlandia L. sensu Bremekamp). Morphological investigations of the taxa are ongoing in order to find support for the many new clades and relationships detected. This study provides a phylogenetic hypothesis with broad sampling across the major lineages of Spermacoceae that can be used to guide future species-level and generic studies.

In this study, foliar and petiole anatomy of several genera was compared to determine whether there are characteristics that can be used to reevaluate the circumscription and taxonomic position of Hamelieae (Rubiaceae). Our sample included a total of 36 species, which were sectioned using conventional embedding and staining methods. From these species, 23 represented six of the seven genera of Hamelieae sensu Robbrecht; Syringantha Standl. was included in order to reevaluate its putative inclusion within Hamelieae. For comparative purposes, the sample also included representative species of tribes Psychotrieae (Rubioideae), the Portlandia informal group (Cinchonoideae), and Gardenieae (Ixoroideae). Our results indicated that foliar and petiole anatomy contained taxonomic information that can be used in systematic studies. Members of Hamelieae shared the following characters: cuticle more than 3 µm, dorsiventral mesophyll, a single palisade parenchyma cell layer, loose spongy parenchyma, raphides, tannins, and vascular tissue of types I, II, or III in the midrib and petiole. Plocaniophyllon Brandegee is unique in having fibers associated with major and minor veins. The petiole vascular tissue has an open arc shape in all studied species except in Randia L., which has a closed cylinder. Hamelieae, Syringantha, and Psychotria L. have raphides, one layer of palisade parenchyma cells, and loose spongy parenchyma, while the other taxa have druses, two layers of palisade parenchyma cells, and compact spongy parenchyma. Bouvardia Salisb. is unique, showing both raphides and druses. Our results show that comparative foliar and petiole anatomy may provide additional characters to be considered in taxonomic and phylogenetic studies within Rubiaceae. There was anatomical support for the inclusion of Syringantha within Hamelieae, while the presence of raphides and the mesophyll attributes suggest an understanding of why Hamelieae was morphologically treated as a member of Rubioideae.

We performed phylogenetic analyses of DNA sequences of three chloroplast markers: rbcL, rps16, and trnT-F, to rigorously test the monophyly of competing circumscriptions of the tribe Ixoreae. Several genera traditionally or currently associated with the type genus Ixora L. were included in the analyses. Ixora as currently circumscribed appears paraphyletic, as many other genera are nested within it with strong support: Captaincookia N. Hallé, Doricera Verdc., Hitoa Nadeaud, Myonima Comm. ex Juss., Sideroxyloides Jacq., Thouarsiora Homolle ex Arènes, and Versteegia Valeton. Further, Aleisanthia Ridl., Aleisanthiopsis Tange, and Greenea Wight & Arn. are more closely related to Ixora and allies than the monotypic genus Scyphiphora C. F. Gaertn. Consequently, Ixoreae fide Andreasen and Bremer (2000) is not monophyletic without an exclusion of Scyphiphora. Ixoreae fide Robbrecht and Manen (2006) is not monophyletic unless Captaincookia and Doricera are included. The monophyly of a morphologically heterogeneous Ixoreae alliance consisting of Ixora and its relatives Aleisanthia, Aleisanthiopsis, and Greenea is, however, strongly supported. In order to recognize monophyletic and morphologically consistent groups, we adopt a narrow circumscription of Ixoreae (including Bemsetia Raf., Captaincookia, Charpentiera Vieill., Doricera, Hitoa, Ixora, Myonima, Pancheria Montrouz., Sideroxyloides, Thouarsiora, Tsiangia But, H. H. Hsue & P. T. Li, and Versteegia), and two new tribes are erected for Aleisanthia Aleisanthiopsis and Greenea, respectively. The Indo-Malesian Aleisanthieae and the pantropical Ixoreae s. str. are sister groups, and the Southeast Asian Greeneeae is sister to the Ixoreae–Aleisanthieae clade.

New generic circumscriptions of the Paleotropical tribe Vanguerieae in the subfamily Ixoroideae s.l. (Rubiaceae) have recently been established as a result of a series of phylogenetic studies conducted by Lantz and Bremer. The genus Canthium Lam. was shown in their study to be highly polyphyletic, and a largely dioecious group was for the first time identified within Vanguerieae. The dioecious group sensu Lantz and Bremer comprises about 140 species classified in eight genera: Canthium (Canthium subg. Bullockia Bridson), Dinocanthium Bremek., Leroya Cavaco, Neoleroya Cavaco, Peponidium (Baill.) Arènes, Pseudopeponidium Homolles ex Arènes, Pyrostria Comm. ex Juss., and Scyphochlamys Balf. f. We sequenced 79 Vanguerieae taxa and performed phylogenetic analyses based on sequence data from two nuclear (ETS and ITS) markers to: (1) pinpoint the phylogenetic positions of the Comorean and Indian Ocean Canthium and the Southeast Asian Canthium confertum Korth. group in Vanguerieae; (2) evaluate the phylogenetic utility of three taxonomic characters (bract type, locule number, and fruit shape) previously and currently used for delimiting genera in the dioecious group; and (3) assess the evolution of functional dioecy in Vanguerieae. The results support a further disintegration of Canthium s.l., as the Comorean and Malagasy Canthium species are shown for the first time to be closely related to Peponidium. Similarly, C. confertum appears to have a close affinity with Cyclophyllum Hook. f. The combined analyses show that the dioecious group can be subdivided into four morphologically distinct clades formally recognized as genera: Bullockia (Bridson) Razafim., Lantz & B. Bremer, here elevated from Canthium subgen. Bullockia Bridson, as well as Cyclophyllum, Peponidium (including all Comorean, Malagasy, and Seychellean Canthium species), and Pyrostria (including Dinocanthium, Leroya, Neoleroya, Pseudopeponidium, and Scyphochlamys). All described species of Canthium subgen. Bullockia are transferred to Bullockia: B. dyscriton (Bullock) Razafim., Lantz & B. Bremer, B. fadenii (Bridson) Razafim., Lantz & B. Bremer, B. impressinervia (Bridson) Razafim., Lantz & B. Bremer, B. mombazensis (Baill.) Razafim., Lantz & B. Bremer, B. pseudosetiflora (Bridson) Razafim., Lantz & B. Bremer, and B. setiflora (Hiern) Razafim., Lantz & B. Bremer. Furthermore, the results seem to point to a single origin of functional dioecy followed by subsequent reversals back to the hermaphroditic conditions at least within the Cyclophyllum–