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Further disintegration and redefinition of Clerodendrum (Lamiaceae): Implications for the understanding of the evolution of an intriguing breeding strategy

TitleFurther disintegration and redefinition of Clerodendrum (Lamiaceae): Implications for the understanding of the evolution of an intriguing breeding strategy
Publication TypeJournal Article
Year of Publication2010
AuthorsYuan Y-W, Mabberley DJ, Steane DA, Olmstead RG
Start Page125
Date Published02/2010

<p>The genus Clerodendrum s.l. is polyphyletic. Although recent studies have resulted in C. subg. Cyclonema and C. sect.<br />
Konocalyx being removed to the resurrected genus Rotheca, and the unispecific genus Huxleya being sunk into Clerodendrum,<br />
it has been unclear whether Clerodendrum as currently circumscribed is monophyletic, particularly in relation to the American<br />
genera Aegiphila, Amasonia, and Tetraclea. This phylogenetic study employs four relatively fast-evolving chloroplast DNA regions,<br />
trnT-L, trnL-F, trnD-T, and trnS-fM, to clarify the generic boundaries of Clerodendrum and its relationship to allied genera.<br />
The results corroborate previous studies that there are three well-supported clades in the currently recognized Clerodendrum: an<br />
Asian clade, an African clade, and a Pantropical Coastal clade. The Asian clade and African clade are sister groups and together<br />
form a monophyletic group. However, the Pantropical Coastal clade is more closely related to the three American genera than it<br />
is to the other two Clerodendrum clades. In addition, a Caribbean species, C. spinosum, is found to be more closely related to the<br />
American genera than it is to any of the three major Clerodendrum groups. These results indicate that Clerodendrum as currently<br />
circumscribed is not monophyletic. We propose to separate the Pantropical Coastal clade and C. spinosum by reviving the genera<br />
Volkameria (including Huxleya) and Ovieda, respectively for these, and to restrict Clerodendrum to the Asian and African clades.<br />
Brief descriptions of the genera to be recognized are provided. All Neotropical &lsquo;Clerodendrum&rsquo; taxa are referred to other genera,<br />
necessitating six new combinations, which are also provided, where required, for two other well-studied Old World Volkameria<br />
species; all names ever used in Ovieda are given their modern placings (two placed newly in synonymy). The study also sheds light<br />
on the evolution of an intriguing breeding strategy that avoids self-pollination or/and sexual interference. This strategy involves<br />
presentation of pollen and stigma in the centre of the flower in a sequential fashion by moving the filaments and style. It appears<br />
to have evolved in the common ancestor of Clerodendrum, Volkameria, Ovieda, Amasonia, Tetraclea, Aegiphila and Kalaharia,<br />
and still occurs in all of these taxa except Aegiphila, where it has been succeeded by a heterostylous system.</p>