Two new genera of Acanthaceae from tropical Africa

Iain Darbyshire,Carrie A Kiel,W R Quentin Luke,Thomas F Daniel,Lucinda A Mcdade

doi:10.1007/s12225-019-9828-z

Abstract

SummaryDNA sequence data, macro-morphological evidence and pollen analysis are used to clarify the phylogenetic placement of two African species of Acanthaceae: Schaueria populifolia C.B.Clarke and Rhinacanthus ndorensis Schweinf. The combined data demonstrate that these species are only distantly related to the genera in which they are currently placed and provide strong support for recognition of new genera to accommodate them. Two new genera are therefore proposed and a taxonomic account is provided for each of these. The first, Champluviera I.Darbysh., T.F.Daniel & C.A.Kiel, is based primarily on S. populifolia but Chlamydocardia nuda C.B.Clarke (= Justicia tigrina Heine) is also included within this new genus based on shared morphological traits, at least one of which is synapomorphic and restricted to these species. Based on molecular evidence, Champluviera is placed in a well-supported clade of several genera that are together sister to the core Isoglossinae lineage of tribe Justicieae. The genus may be recognised morphologically by the combination of a dense spiciform terminal thyrse with the bracts, bracteoles and calyx lobes all slender and closely resembling one another; a bilabiate corolla lacking a rugula and with intricate speckling or striping on the lips; and, in particular, the putatively synapomorphic trait of anther thecae with broad, flattened, basal appendages that have an irregularly toothed fringe. The second new genus, Kenyacanthus I.Darbysh. & C.A.Kiel, is based on R. ndorensis and is so far thought to be monospecific. It is placed between core Diclipterinae and Monechma Group II within the expanded subtribe Diclipterinae in tribe Justicieae. Kenyacanthus can be recognised morphologically by having the combination of a trailing or procumbent habit; fasciculate inflorescences; bracts, bracteoles and calyces with hyaline margins; a bilabiate corolla with a slender cylindrical tube longer than the limb and with a shallow rugula; stenotribic flowers, with the stamens held against the lower lip; and anthers with only slightly offset thecae that lack appendages.

Highlights

With at least 2000 species and a nearly worldwide distribution, the Justicieae lineage of the Acanthaceae has long challenged taxonomists
The topologies returned by Bayesian inference (BI) and maximum likelihood (ML) are congruent and are congruent with the results of all earlier studies of Justicieae (e.g., McDade et al 2000, 2018; Kiel et al 2006, 2017; Daniel et al 2008; Côrtes et al 2016)
We emphasise here the placement of the two focal taxa and do not reiterate the relationships established in earlier studies, a more complete review of relationships within Justicieae will be presented in a forthcoming paper (Kiel et al in prep)

Summary

Introduction

With at least 2000 species and a nearly worldwide distribution, the Justicieae lineage of the Acanthaceae has long challenged taxonomists. We propose solutions for two such taxonomic problems involving the African plants Schaueria populifolia C.B.Clarke and Rhinacanthus ndorensis Schweinf. The genus is exclusively New World (NW) in distribution with the notable exception of S. populifolia C.B.Clarke (1900a: 242), which is found in the lowland rainforests of eastern Nigeria, Bioko and western and southern Cameroon. Daniel et al (2008) noted that there are otherwise no genera of the Tetramerium lineage common to both the Old World (OW) and NW. As such, it would be remarkable if this African species were a Schaueria

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