Molecular phylogeny ofTrigonostemonand its relatives (Euphorbiaceae)

Abstract

Trigonostemon, Dimorphocalyx, Tritaxis and Ostodes are tropical Asian genera that are very similar in morphology. The former three genera have been treated either as a single genus Trigonostemon s.l. or as separate genera. A molecular phylogeny based on the nuclear ITS and chloroplast trnK intron, trnT‐L and trnL‐F sequences reveals that Trigonostemon is a monophyletic group, and Dimorphocalyx and Tritaxis together form another monophyletic group separate from Trigonostemon. Within the genus Trigonostemon, a strong correlation between the molecular phylogeny and pollen morphology was found. It demonstrates two potential evolutionary directions for the common “croton pattern” ornamentation of pollen in the genus: the subunits that form the “croton pattern” ornamentation tend to reduce to spines or they tend to merge in the later‐developed groups. The correlation between the molecular phylogeny and macromorphology of Trigonostemon is discussed, and a new infrageneric classification with four sections is provided. Dimorphocalyx is reduced to Tritaxis, the older generic name.

An overlooked new variety of Tritaxis glabella from India with a note on the consequent new synonyms of Croton lawianus (Euphorbiaceae)

“…The Indo-Malesian genus Tritaxis Baill. (previously Dimorphocalyx Thwaites), extending to Australia, comprises 16 species of which 4 species and two varieties are known to occur in India (3). The genus Croton L. comprises 750-1000 species, distributed in the tropics and subtropics of both Old and New Worlds (4).…”

Weda, a new genus with two new species of Euphorbiaceae‐Crotonoideae from Halmahera (North Maluku, Indonesia) and phylogenetic relationships of the Australasian tribe Ricinocarpeae

“…Clade C2 of Crotonoideae with inaperturate pollen presently includes 45–52 (varying according to circumscriptions) mostly Old World genera grouped into the non‐monophyletic tribes Codiaeae (Pax) Hutch., Ricinocarpeae, Ricinodendreae (Pax) Hutch., and Aleuritidae Hurus. Relatively few molecular phylogenetic studies have sampled within clade C2 (i.e., Wurdack et al, 2005; Tokuoka, 2007; Cheek et al, 2016; Yu et al, 2019). Although our clade C2 taxon sampling is the most comprehensive to date (48 genera, including 10 new to GenBank, but missing Benoistia H.Perrier & Leandri, Loerzingia Airy Shaw [= Deutzianthus Gagnep.…”

“…Clade C2 of Crotonoideae with inaperturate pollen presently includes 45-52 (varying according to circumscriptions) mostly Old World genera grouped into the non-monophyletic tribes Codiaeae (Pax) Hutch., Ricinocarpeae, Ricinodendreae (Pax) Hutch., and Aleuritidae Hurus. Relatively few molecular phylogenetic studies have sampled within clade C2 (i.e., Wurdack et al, 2005;Tokuoka, 2007;Cheek et al, 2016;Yu et al, 2019 , 2014]), resolution remains poor, which would benefit from a phylogenomic approach. Among new insights are that Vernicia would be paraphyletic if reunited with Reutealis Airy Shaw, as was proposed by Webster (2014), unless Deutzianthus (with perhaps Loerzingia included as synonym) was not also reduced.…”