Reduction of Breynia subgenus Hemisauropus to B . section Cryptogynium and discussion of the B . quadrangularis complex ( Phyllanthaceae )

Breynia subgenus Hemisauropus is reduced to Breynia section Cryptogynium. Arguments are given to regard the Breynia quadrangularis complex as a single species.


INTRODUCTION
The genera Phyllanthus L., Breynia J.R.Forst.& G.Forst., Glochidion J.R.Forst.& G.Forst. and Sauropus Blume form a clade in the phylogeny of the Phyllanthaceae (Kathriarachchi et al. 2006), where Phyllanthus is paraphyletic.Two options exist to address the paraphyly.Phyllanthus can be made monophyletic by either subsuming the non-included genera into a gigantic Phyllanthus (Hoffmann et al. 2006) or Phyllanthus may be split into morphologically recognisable monophyletic genera (Van Welzen et al. 2014).Van Welzen et al. (2014) opt for the latter solution and based on phylogenetic evidence (Pruesapan et al. 2012) they recognised the genera Synostemon F.Muell.(formerly united with Sauropus) and Breynia (including the non-Synostemon part of Sauropus, also known as Sauropus s.str.).
The recent phylogeny of Breynia (Pruesapan et al. 2012) shows that the clade splits basally into two groups, recognised as the subgenera Breynia and Sauropus Welzen & Pruesapan.The subgenus Breynia clade splits again in two groups, recognised as section Breynia (equalling the genus Breynia before union with Sauropus) and section Cryptogynium (Müll.Arg.)Welzen & Pruesapan (Van Welzen et al. 2014).The infrageneric classification thus reflects the phylogeny.Hoffmann et al. (2006) published their recommendation to unite all genera into Phyllanthus, Chakrabarty & Balakrishnan (2009) made all combinations under Phyllanthus for all Indian species of Breynia and Sauropus, reverting these to Breynia (Chakrabarty & Balakrishnan 2012) as soon as Pruesapan et al. (2012) published the idea to subdivide Phyllanthus.

Shortly after
Recently, Chakrabarty & Balakrishnan (2015) raised Breynia section Cryptogynium (Van Welzen et al. 2014) to subgeneric rank as B. subgenus Hemisauropus (Müll.Arg.)Chakrab.& N.P.Balakr.The only argument given is that it facilitates the recognition of the small-leaved species of Breynia.This decision is unfortunate for three reasons.
The small-leaved group of Breynia species also contains species with larger leaves (e.g., B. pierrei (Beille) Welzen & Pruesapan, B. subterblanca (C.E.C.Fisch.)C.E.C.Fisch.)and is, as a group, not really recognisable by the size of the leaves.Moreover, section Breynia, the sister-group of section Cryptogynium, also only comprises small-leaved species.Therefore, the argument by Chakrabarty & Balakrishnan (2015) is invalid.
The raise to subgeneric level disrupts the phylogenetic information (Pruesapan et al. 2012, Van Welzen et al. 2014), because Chakrabarty & Balakrishnan (2015) only retain section Breynia, while section Cryptogynium (their subgenus Hemisauropus) is of equal standing.In their classification it seems that their subgenus Hemisauropus equals subgenus Sauropus and might be a sister-group, which it is not.
Finally, the name Hemisauropus, is very unfortunate (but nomenclaturally necessary at subgenus level).In former classifications (e.g., Airy Shaw 1969), Hemisauropus only referred to a part of current section Cryptogynium, containing a group of species with staminate flowers with partly infolded sepals grown together via the midrib, absent scales and large stamens.However, this Hemisauropus group, though recognisable, was found to be polyphyletic as The best way forward will be to use molecular data in a phylogeographic approach to see if the complex contains a single or multiple species.Until such studies have been performed, disagreements like these are likely to persist.