Observations on Thamnidiaceae. VII. Helicostylum and a New Genus Kirkia

Abstract

The genus Helicostylum was restricted to two species, H. elegans and H. pulchrum, based on the phy? logenetic species concept. Helicostylum species were distinguished from other genera of Thamnidiaceae by the production of 1) relatively large, multispored, de- liquesent-walled sporangia at the apices of the spo- rangiophores and 2) pedicellate, relatively small, per- sistent-walled sporangiola laterally from the sporan- giophore itself or from lateral branchlets having elon- gate, sterile, spine-like terminations. In some cases a given sporangiophore bears only sporangia or spor? angiola. The lateral, fertile branches arose singly, in pairs, or in verticels or pseudoverticels of three to 20. Zygospores were described for the first time for H. pulchrum. A new genus Kirkia was based on H. cordense, which lacks spinelike fertile branches and has an op- timal growth temperature of 25 C vs slightly below 20 C for species of Helicostylum. A cladistic analysis using representative species of all sporangiate Thamnidi? aceae demonstrated that Helicostylum and Kirkia re- sided in separate clades. Selected strains of all species of Helicostylum were included in the analysis. Helicos? tylum venustellum was considered a synonym of H. pul? chrum. All taxa were illustrated with line drawings. Keys were provided to genera and species, and an extensive list of synonyms was presented.