Systematics and biogeography of the genus <i>Pseudocodium</i> (Bryopsidales, Chlorophyta), including the description of <i>P. natalense</i> sp. nov. from South Africa

Abstract

This study examines the diversity of Pseudocodium, a small green algal genus assigned to its own family in the order Bryopsidales. The included species are characterized by uncalcified thalli with a medulla composed of a limited number of interwoven siphons that form a cortex of distinctive utricles toward the periphery. Detailed morphological descriptions are provided for all known species. A combination of characters relating to general habit, morphology of the axes, apices and utricles distinguishes all species easily. Re-examination of Indonesian and Papua New Guinean specimens, previously reported as Pseudocodium floridanum, reveals that they belong to the recently described Pseudocodium okinawense. South African specimens formerly attributed to P. floridanum are described as a new species, Pseudocodium. natalense. Pseudocodium australasicum, a species endemic to southern Australia, does not fit the generic concept of Pseudocodium in that it does not possess a cortex composed of utricles. Putative reproductive structures have thus far only been reported for P. floridanum. Observations on Pseudocodium devriesii and P. natalense reveal very similar spherical to irregular structures formed laterally on medullary siphons in the axils of peripheral utricles. Interestingly, and confirming the earlier observations of Dawes & Mathieson, no basal cross wall is formed at the base of the reproductive structures. Instead, a translucent plug at the base of the reproductive structures prevents the cytoplasm from leaking. This suggests that Pseudocodium is not holocarpic, unlike most Halimedineae. DNA sequences of rbcL and tufA are presented for all species and the resulting phylogenies are used as a framework to study the evolution of morphological features as well as the biogeography of the genus, both at the global scale and within the Indian Ocean