Towards a taxonomic revision of Tradescantia subg. Campelia (Commelinaceae) I: sectional arrangement and revision of T. sect. Rhoeo

Abstract

Background and aims – Tradescantia subg. Campelia is the most morphologically diverse and one of the most taxonomically complex subgenera of Tradescantia. This makes taxonomic efforts within this group challenging, especially due to the current lack of formal recognition of monophyletic infrageneric groups and their widespread horticultural use.

Thus, continuing our previous efforts, we provide a sectional classification for the subgenus, combined with a taxonomic revision of T. sect. Rhoeo. Material and methods – This study was based on a combination of systematic, micro- and macromorphological, palynological, and horticultural data.

We analysed type specimens, protologues, field images, and herbarium sheets of all names, in addition to growing all species and cultivars. We have also reviewed previously published palynological data for the recognised species and provided all needed corrections and updates, in addition to a novel interpretation of their taxonomic relevance. Key results – We propose the subdivision of T. subg.

Campelia into four sections: 1) T. sect. Campelia; 2) T. sect. Corinna; 3) T. sect.

Cymbispatha; and 4) T. sect. Rhoeo. These sections are supported by a combination of molecular, micro- and macromorphological, anatomical, palynological, cytological, and phytochemical data.

Within T. sect. Rhoeo, we accept two species, T. spathacea and the newly recognised T. concolor. Horticulturally, we propose the T. spathacea Bantam Group, including five dwarf cultivars, while T. spathacea ‘Vittata’ is the only regular-sized variegated cultivar of wild origin.

We also explore the palynology of T. sect. Rhoeo, highlighting palynotaxonomically relevant characters in Tradescantia and T. subg. Campelia.

Conclusions – We lay the groundwork for ongoing and future studies on T. subg. Campelia. The recognition of sections within this subgenus will facilitate identification, communication, and enable the recognition of functional taxonomic groups for future systematic and taxonomic studies.

The combination of palynology and horticulture provides further support for the taxonomy and systematics of Tradescantia, and should be consistently included in future studies of the group.