A Reconsideration of the Infrageneric Classification of Homalium Jacq. (Salicaceae)

Abstract

Homalium Jacq. (Salicaceae) is widespread in tropical regions and includes considerable diversity in floral morphology. Its modern infrageneric classification is complex, including two subgenera and nine sections. Morphological variation within the genus is described, and an emended classification including ten sections is proposed. Subgenera have been defined by stamen number : subg. Homalium has stamens in fascicles of 2 to 12, while subg. Blackwellia (Benth.) Warb. has one stamen per petal. These subgenera are not natural groups; since the relationships of some sections are uncertain, recognition of subgenera may not be of value and is not upheld here. Sect. Eumyriantheia Warb. is polyphyletic ; it is herein restricted to Malagasy species, while sect. Polyanthera Warb. is revived for fasciculate-stamened species from Asia to the Pacific region. Also, three Malagasy species formerly placed within sect. Blackwellia Benth. (Homalium brachystylis (Tul.) Baill., Homalium longistaminum H. Perrier, and Homalium planiflorum (Boivin ex Tul.) Baill.) are transferred to sect. Odontolobus Warb. Several problematic species are individually discussed. RésuméAPPLEQUIST, W.L. (2016). Une révision de la classification infragénérique du genre Homalium Jacq. (Salicaceae). Candollea 71 : 231-256. En anglais, résumés anglais et français.

A revision of Homalium sect. Rhodonisa (Salicaceae) endemic to Madagascar

“…Materials examined included herbarium specimens at MO, duplicates of MO collections not yet distributed, and specimens from P seen during a visit, with a few potential types received on loan. In addition, images of types held by other institutions available through the JSTOR Plants website [https://plants.jstor.org] were observed, and images of some specimens were obtained from G. Standard taxonomic procedures were followed, consistent with the recent revision of other sections of Homalium in Madagascar (Applequist, 2016a(Applequist, , 2018a(Applequist, , 2018bWassel & Applequist, 2020).…”

“…Eumyriantheia and Nisa, but often elongated, narrow, ridged calyx cups, and sometimes also small "Blackwellia-like" anthers with subglobose locules. These species are not easily classed as belonging to either group of sections, which is one reason for this author's preference not to recognize subgenera (Applequist, 2016a). Sleumer (1973) recognized two red-flowered species, H. sanguineum (Boivin ex Tul.)…”

“…vs. fasciculate stamens (subg. Homalium) appears to be homoplasious (Applequist, 2016a). Before recent re-evaluation of the Malagasy species, about 150 species had been recognized within the genus (Applequist, 2013).…”

“…The greatest sectional diversity is ascribed to Madagascar, with six sections, five of which are considered endemic following the restriction of sect. Eumyriantheia to only Malagasy species (Applequist, 2016a). The Malagasy species were revised by Sleumer (1973), who recognized a total of 28 species in Madagascar.…”

“…This section is distinguished by solitary stamens, petals usually accrescent and larger than the sepals (in contrast to sect. Nisa, where the opposite is true), and persistent bracts and bracteoles (Applequist, 2016a). The last taxonomic revision of sect.…”