The morphology and reproductive structures of Mediterranean species of the genus Nemastoma J. Agardh, nom. cons. (Nemastomataceae, Nemastomatales): Nemastoma dichotomum and N. dumontioides

Abstract

We investigated a collection of Nemastoma J. Agardh, nom. cons. (Nemastomatales, Rhodophyta), including the Mediterranean type material of species described by J. Agardh, Kutzing and Ercegovic, and recent specimens from the Mediterranean Sea, Adriatic Sea and northeastern Atlantic Ocean. Based on their habit and vegetative and reproductive structures, we confirm that: (i) all the Mediterranean specimens studied belong to the genus Nemastoma; (ii) two species of Nemastoma co-exist in the Mediterranean Sea: (a) N. dichotomum, which is characterized by great plasticity of habit, a cartilaginous thallus in its basal and middle parts, and presumed reproduction exclusively by apomixis; and (b) N. dumontioides, which is characterized by a regularly pseudodichotomous, saccate-membranous thallus, and which reproduces both sexually and probably apomictically; and (iii) the Atlantic specimens attributed to N. dichotomum belong to other genera, and so, N. dichotomum is probably endemic to the Mediterranean Sea. Thus, three species described by Kutzing have been reduced to vari eties of Nemastoma dichotomum: (a) var. biasolettianum (Kutzing) Rodriguez-Prieto, Verlaque et Verges comb. nov. et stat. nov., with ligulate upper parts, (b) var. caulescens (Kutzing) Rodriguez-Prieto, Verlaque et Verges comb. nov. et stat. nov., with wedge-shaped upper parts, and (c) var. incrassatum (Kutzing) Rodriguez-Prieto, Ver laque et Verges comb. nov. et stat. nov., with spathulate upper parts. Finally, Nemastoma constrictum and N. constrictum var. longitrichogynum are placed in synonymy with N. dichotomum var. caulescens.