Retiniphyllum

Retiniphyllum is a genus of flowering plants in the family Rubiaceae and contains 20 species.[1] It is the only genus in the tribe Retiniphylleae. The representatives are shrubs or small trees that grow in white sand soils in tropical South America. They are mainly distributed in the Guayana Region (Venezuela) but also occur in the Amazon Basin, the eastern Andes and central and eastern Brasil.[2]

Retiniphyllum
Scientific classification
Kingdom: Plantae
Clade: Tracheophytes
Clade: Angiosperms
Clade: Eudicots
Clade: Asterids
Order: Gentianales
Family: Rubiaceae
Subfamily: Ixoroideae
Tribe: Retiniphylleae
Genus: Retiniphyllum
Humb. & Bonpl.
Type species
Retiniphyllum secundiflorum
Humb. & Bonpl.
Synonyms

Description

The species exhibit a character that is not common in the family Rubiaceae, viz. the presence of two collateral and pendulous ovules per locule. The shrubs or trees have apical buds with abundant resin. Each flower is subtended by a bracteole and the corollas are contorted. Stamens are reflexed in anthesis and have basal and apical sterile appendages. Many species also exhibit secondary pollen presentation. The 5-locular ovary contains two ovules per locule. The drupaceous fruits contain pyrenes with one seed due to the abortion of one ovule.[2]

Taxonomy

Retiniphyllum was placed in the subfamily Rubioideae in the earliest systems of classification due to the misinterpretation of the bi-ovulated locules. William Jackson Hooker established the tribe Retiniphylleae in 1873 and included the genera Retiniphyllum and Kutchubaea. The classification of the group remained difficult for a long time, which resulted in the placement of the genus Retiniphyllum in different tribes and subfamilies of Rubiaceae. Molecular studies place the genus in an isolated clade of the Ixoroideae related to paleotropical representatives.[3][4] The monophyly of the tribe Retiniphylleae has been confirmed and the tribe is placed as a clade within the subfamily Ixoroideae.[2]

The genera Botryarrhena and Scyphiphora were tentatively included in the tribe Retiniphylleae by Robbrecht (1988).[5] However, molecular data suggest that neither are related to Retiniphyllum.[2] Botryarrhena is resolved within the Alibertia group, sister to Stachyarrhena in a clade with the genera Alibertia, Borojoa and Kutchubaea. The monotypic genus Scyphiphora is sister to a clade that includes the tribe Ixoreae and Vanguerieae.[2]

Species
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References
  1. "Retiniphyllum in the World Checklist of Rubiaceae". Retrieved 5 February 2018.
  2. Cortés-B R, Delprete PG, Motley TJ (2009). "Phylogenetic placement of the tribe Retiniphylleae among the subfamily Ixoroideae (Rubiaceae)". Annals of the Missouri Botanical Garden. 96 (1): 61–67. doi:10.3417/2006198.
  3. Andersson L, Rova JH (1999). "The rps16 intron and the phylogeny of the Rubioideae (Rubiaceae)". Plant Systematics and Evolution. 214: 161–186. doi:10.1007/bf00985737.
  4. Rova JH, Delprete PG, Andersson L, Albert VA (2002). "A trnL-F cpDNA sequence study of the Condamineeae-Rondeletieeae-Sipaneeae complex with implications on the phylogeny of the Rubiaceae". American Journal of Botany. 89 (1): 145–159. doi:10.3732/ajb.89.1.145. PMID 21669722.
  5. Robbrecht E (1988). "Tropical woody Rubiaceae". Opera Botanica Belgica. 1: 1–271.
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