Morphology and molecules support the new monotypic genus Parainvolucrella (Rubiaceae) from Asia.

Yi-Da Xu,Rui-Jiang Wang,Ming-Deng Yuan

doi:10.3897/phytokeys.180.67624

Abstract

Parainvolucrella R.J. Wang, a new monotypic genus for P.scabra (Wall. ex Kurz) M.D.Yuan & R.J.Wang, new combination, is segregated from the Hedyotis-Oldenlandia complex, based on morphological and molecular evidence. Phylogenetically, the new genus is sister to Scleromitrion, from which it differs by a combination of morphological characters: herbaceous habit, terminal inflorescence with subtended leaves, heterostylous flowers, indehiscent fruits and pollen with double microreticulate tectum. A key to the genera of the Hedyotis-Oldenlandia complex in China is provided for further identification.

Highlights

As one of the largest species groups of the family Rubiaceae, the Hedyotis-Oldenlandia complex contains hundreds of species distributed in the tropical and subtropical region worldwide
The plant habit, stipule shape, inflorescence position, flower distyly and the dehiscent pattern of the fruits are of diagnostic significance in the different genera of the Hedyotis-Oldenlandia complex (Dutta and Deb 2004)
Hedyotis scabra differs from Scleromitrion by the terminal inflorescences with involucral leaves, the heterostylous flowers, pollen grains tectum double microreticulate, with psilate suprareticulum and microechinate infrareticulum and indehiscent fruits

Summary

Introduction

As one of the largest species groups of the family Rubiaceae, the Hedyotis-Oldenlandia complex contains hundreds of species distributed in the tropical and subtropical region worldwide. Due to morphological intermediacy and homoplasy, systematic studies in herbaceous Rubiaceae are very difficult (Gibbons 2020). Capsular fruits made some studies treat this complex as one genus, Hedyotis L., in a broad sense (Lamarck 1792; Fosberg and Sachet 1991; Dutta and Deb 2004; Chen and Taylor 2011). Morphological differences in habit, inflorescence position, homo- or heterostylous flowers, dehiscent or indehiscent fruits, as well as the shape and ornamentation of seeds and pollen, provide unquestionable evidence to separate this complex into several small genera (Bremekamp 1952; Terrell et al 1986; Terrell and Robinson 2003). The Hedyotis species in China fall into the following genera of Debia Neupane & N.Wikstr., Dimetia (Wight & Arn.) Meisn., Edrastima Raf., Hedyotis, Involucrella The Hedyotis species in China fall into the following genera of Debia Neupane & N.Wikstr., Dimetia (Wight & Arn.) Meisn., Edrastima Raf., Hedyotis, Involucrella (Benth. & Hook.f.) Neupane & N.Wikstr., Leptopetalum Hook. & Arn., Oldenlandia L. and Scleromitrion (Wight & Arn.) Meisn. (Neupane et al 2015; Wang 2018)

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