Morphology of the invasive 'Carpobrotus' (Aizoaceae) in Europe: Malta as a case study

Stephen Mifsud

doi:10.5209/mbot.71195

Abstract

Since the late 19th century, different taxonomic views have been reported for Carpobrotus species occurring in the Maltese Islands, where the latest treatments imply two varieties of C. edulis and the doubtful occurrence of C. acinaciformis. Taxonomic inconsistencies are possibly derived from the poor understanding or misinterpretation of morphological characters. Moreover, the hybridogenous morphotypes resulting from horticultural advances make the determination of Carpobrotus even harder, especially with the application of outdated identification keys which do not take hybrids into account. The difficulty in determining Carpobrotus spp. has been expressed in several recent accounts within the Mediterranean region. A taxonomic investigation was carried out by applying eleven morphological characters adopted from recent monographs on 25 populations present in Malta. Three taxonomic units have been retrieved from the analyzed sample, where C. acinaciformis s.l. has been confirmed to represent all the purple-flowering populations and C. edulis s.s. for the yellow-flowering ones. Emphasis was given on the interpretation and understanding of distinctive morphological characters by employing a standardized method of assessment aided by images. This comparative morphological study resulted in a new characteristic in the leaves of C. edulis, by which it could be easily distinguished from C. acinaciformis in the vegetative state. A detailed discussion about the two different morphotypes of C. acinaciformis s.l. and dichotomous keys to distinguish Carpobrotus taxa are also provided.

Highlights

Carpobrotus are native to coastal areas of Cape Town, South Africa and were introduced in the Mediterranean region in the 17th century as ornamental garden plants (Preston & Sell, 1988), which gradually spread further north and became invasive in many coastal areas, in the Mediterranean but throughout the five continents as well explained in great detail by Campoy et al (2018)
Three principal outcomes resulted from this investigation: i) a sound understanding of the three morphotypes of Carpobrotus occurring in the Maltese Islands; ii) a better interpretation of the most taxonomically significant characters used in the field, and iii) an unreported morphological characteristic that distinguishes Carpobrotus taxa in the vegetative state without the need for any dissection
Both C. edulis and C. acinaciformis s.l. have been confirmed as had already been indicated (Mifsud, 2019), the latter has been found to be represented by two distinct morphotypes as discussed below

Summary

Introduction

Carpobrotus are native to coastal areas of Cape Town, South Africa and were introduced in the Mediterranean region in the 17th century as ornamental garden plants (Preston & Sell, 1988), which gradually spread further north and became invasive in many coastal areas, in the Mediterranean but throughout the five continents as well explained in great detail by Campoy et al (2018). The taxonomic repertoire of Carpobrotus spp. is quite unstable for Malta and has been subjective to different taxonomists. The difficulty in determining Carpobrotus plants is exhibited in Malta (see history chapter below) and in many parts of the Mediterranean region. The morphological distinction between the two main European species Carpobrotus acinaciformis (L.) L. Hybridization between the two species had been expressed (Suehs et al, 2004a,b), making their determination even harder (Campoy et al, 2018) due to broader overlapping of characters

Methods

Results

Discussion

Conclusion