Hubera vitiensis (Seem.) Chaowasku, 2012

Chaowasku, T, Johnson, DM, van der Ham, RWJM & Chatrou, LW, 2012, Characterization of Hubera (Annonaceae), a new genus segregated from Polyalthia and allied to Miliusa, Phytotaxa 69, pp. 33-56 : 51-52

27. Hubera vitiensis (Seem.) Chaowasku , comb. nov.

Basionym: Polyalthia vitiensis Seemann (1865: 4) .

Distribution: ⎯ Fiji.

Notes: ⎯Study of herbarium specimens of this species (see Table 1) was the basis for this transfer; no DNA was available for this species.

Several species (e.g. H. henrici , H. korinti , H. nitidissima , H. perrieri , H. stuhlmannii , H. vitiensis ) exhibit domatia on the lower leaf surface at the axils where the secondary veins meet the primary veins ( Figs. 5A–D; see comparisons of lower leaf surface without domatia in Figs. 5E–H). They are characterized by a tuft of aggregated hairs visible to the naked eye. In Annonaceae , this kind of domatium has been reported to occur in Mitrephora Hooker & Thomson (1855: 112) ( Weerasooriya & Saunders 2010), which is also a member of the Miliuseae , and Annona Linnaeus (1753: 536) [including Rollinia Saint-Hilaire (1824: 28) ] ( Van den Bos et al. 1989), a member of the subfamily Annonoideae ( Chatrou et al. 2012) .

The genus Miliusa was recovered as sister to Hubera . So far, no morphological synapomorphy linking these genera has been observed. They only share some characters considered as symplesiomorphies, such as reticulate tertiary leaf venation and pollen with verrucate to rugulate ornamentation (cerebroid sensu Mols et al. 2004b) and germination zone(s) characterized by enlargements/reductions of the intine sublayers ( Chaowasku et al. 2008).

Among genera of Malmeoideae , Hubera exhibits the widest distribution, ranging from East Africa and Madagascar across southern and southeastern Asia through Malesia and the southwestern Pacific. It is the only genus of Miliuseae that occurs in Madagascar and East Africa. Phylogenetic analysis of Hubera ( Fig. 1) shows some clear biogeographic patterns. The Afro-Madagascan species are grouped together in a strongly supported clade (clade A2), as do the species occurring in the Austro-Papuasian area, which are clustered, with strong support, in clade A1. The biogeographic scenario explaining this distribution will be the focus of another study.

Schatz & Le Thomas (1990) revised Polyalthia species occurring in Madagascar and distinguished five informal groups (groups A–E) based on macromorphological and pollen characters. Species of groups B and C possess monosulcate pollen and were found to form a strongly supported clade (now transferred to Fenerivia ) recovered outside Miliuseae ( Saunders et al. 2011) , which is congruent with the phylogenetic results. Genera outside Miliuseae exhibit monosulcate pollen, whereas genera belonging to Miliuseae possess cryptoaperturate/disulculate pollen ( Chaowasku et al. 2012). Species of groups A, D, and E have cryptoaperturate pollen, and their membership in Hubera , which is a member of the Miliuseae , was thus not unexpected.

It is generally difficult to distinguish Hubera from Fenerivia using only macromorphology. Both genera share some similar morphological features, e.g. axillary inflorescences, uniovulate carpels, and spiniform(- flattened peg) endosperm ruminations ( Schatz & Le Thomas 1990). However, Fenerivia possesses a more pronounced seed raphe that is rib-like ( Saunders et al. 2011), whereas that of Hubera is flat to slightly raised ( Fig. 4a). In addition, Fenerivia exhibits a pronounced (± thickened) receptacle rim (vestigial calyx flange sensu Saunders et al. 2011). This feature is considered one of the diagnostic characters of Fenerivia . It is absent (or rarely slightly observed) in Hubera . Nevertheless, the presence of domatia on the lower leaf surface should be a primary character in distinguishing Madagascan Hubera from Fenerivia because the latter does not possess this character, whereas Hubera species formerly known as Polyalthia group A of Schatz & Le Thomas (1990) do. Domatia on the lower leaf surface can also be used to quickly distinguish certain Afro- Asian species of Hubera from Polyalthia s.s. and other genera formerly known as Polyalthia . Another consequence of this study is elimination of Polyalthia s.s. from the floras of Africa and Madagascar; thus, it is strictly a genus of Australasia.