A taxonomic revision of Brachychiton (Sterculiaceae)

Abstract

Brachychiton Schott & Endl. has previously been included under Sterculia and its generic status has been uncertain. Characters of the follicles, seed coats and embryo strongly support the retention of Brachychiton as a separate genus.

The genus comprises five sections, including one new section, Oxystele Guymer. Characters useful in identification and classification are reassessed and those found to be of most significance are described in detail and illustrated. Chromosome numbers of 2n = 40 for 12 species are recorded for the first time. Keys for the identification of taxa are given. Detailed new descriptions, distribution (including a map based on herbarium specimens), ecology, conservation status and relationship are provided for each taxon, and most taxa are illustrated. Taxa described as new are: B. acuminatus, B. albidus, B. chillagoensis, B. collinus, B. compactus, B. diversifolius subsp. orientalis, B. fitzgeraldianus, B. grandiflorus, B. megaphyllus, B. muellerianus, B. multicaulis, B. obtusilobus, B. populneus subsp. trilobus, B. spectabilis, B. tridentatus and B. xanthophyllus. The following five new combinations are made: B. garrawayae (Bailey) Guymer, B. tuberculatus (W. Fitzg.) Guymer, B. viridiflorus (W. Fitzg.) Guymer, B. viscidulus (W. Fitzg.) Guymer and B. vitifolius (Bailey) Guymer.

Naturally occurring hybrids within the genus are frequent between partially sympatric species. Eight hybrids are recorded and described: B. x allochrous, B. x carneus, B. x excellens, B. x hirtellus, B. x incarnatus, B. x roseus, B. x turgidulus and B. x vinicolor.