Mezleriopsis 1+2: Introduction and Aims and Objectives

06 Jul, 2023

DRAFT VERSION, updated 2023-07-09

1. Introduction

The section Mezleriopsis (Campanulaceae), following T.G. Lammers’ circumscription, are a group of Lobelia species from Southern Africa. With the exception of Lobelia sonderiana, which is somewhat cosmopolitan in this region, the species are considered to be range-restricted habitat specialists. Where multiple populations occur, these occurrences are starkly disjunct, due to a lack of habitat continuity. Historically, collections were widely made of species bearing the current names as well as a slew of synonyms and potentially misapplied names. Contemporarily, however, these species are relatively seldom seen.

There is thus a paucity¹ of current information combined with a degree of taxonomic uncertainty owing to the proliferation of names and historical reassignments. The first aim of this work is therefore to analyse the available descriptions, locality information etc. to provide context for historical collections and herbarium specimens such that these can be effectively mapped in terms of their relationships to one another temporally and spatially.

The second aim of this work draws on the conclusions of the first – it is to provide guidance to the identification of these species, and by extension, those species with which they may be confused or have some other relationship with.

Historically, members of the Lobelioideae have been distinguished and taxonomies assigned based on morphological characteristics as well as biogeographical factors. Many of the morphological characteristics have been related to relatively minute details such as seed coat form and other parameters of the inflorescence and infructescence. Studies of the molecular phylogeny are currently shedding more light on the genetic relationships between species and appear to show that many species are members of polyphyletic genera and sections.

Whilst not entirely invalidating taxonomies based on morphology and biogeography, in my opinion it highlights the need for practical guidance around identification of species based on a holistic appraisal of the available evidence – including molecular data, smaller-scale habitat observations, conspicuous morphological characteristics as well as biogeographical considerations. In the Southern African context, a clearer understanding and description of the different taxa, inclusive of what idiosyncrasies may remain, will allow for more informed decision-making around conservation and management. A wider appreciation and awareness of these taxa would be an additional benefit and will provide more data with which to take next steps.

This is also part of the reason why this work includes a number of species which have some features in common with the Mezleriopsis taxa. In particular it is worth highlighting at this stage corolla shape, which is shared notably with Lobelia jasionoides, Lobelia muscoides and Wimmerella secunda, as seen below.

Figure 1: From left to right, L. eckloniana (Gigi Laidler), L. jasionoides var. sparsiflora (Felix Riegel), L. muscoides (lennartn), W. secunda (linkie). All photos are CC-BY-NC of the respective authors on iNaturalist.

Another commonality is a preference for wet sites or a relationship to water such as seasonal inundation. As with the Mezleriopsis themselves, these do not constitute grounds for a taxonomic appraisal per se but are of interest from a field identification perspective.

There is also a conservation dimension to this work: under various names, members of this group have been historically collected in habitats, such as seasonal wetlands, which have been significantly impacted by human development. Many of the original collection locations are either entirely turned over to the built environment or have otherwise been significantly transformed. Others may yet come under pressure in the future. Taxonomic uncertainty as well as the generally inconspicuous nature of these plants places them under threat of oversight in the remaining locations where they persist.

The case of Lobelia filicaulis² illustrates this well – an apparent annual, rising from seasonally wet limestone flats along the Zwartkops river around Gqeberha and Kariega in the Eastern Cape, it was considered extinct until its rediscovery in 2018. This site is currently threatened by urban expansion and associated habitat transformation due to human activities such as grazing, water pollution etc. This population therefore remains critically endangered.

2. Aims and objectives

• Detail the original and additional descriptions available for the species and the various synonymous taxa given at different stages.
  • Analyse available iNaturalist and herbarium records in the context of the above.
  • A small number of observations have in the recent years been made of unknown species which bear strong resemblance to the others in Mezleriopsis. These observations will also be investigated.
• Compile the best understanding of the current status with a mind to field identification and recommend future work.

Footnotes