OBSERVATIONS ON THAMNIDIACEAE .7. HELICOSTYLUM AND A NEW GENUS KIRKIA

The genus Helicostylum was restricted to two species, H. elegans and H . pulchrum, based on the phylogenetic species concept. Helicostylum sp ecies were distinguished from other genera of Thamnidiaceae by the pro duction of 1) relatively large, multispored, deliquesent-walled sporan gia at the apices of the sporangiophores and 2) pedicellate, relativel y small, persistent-walled sporangiola laterally from the sporangiopho re itself or from lateral branchlets having elongate, sterile, spine-l ike terminations. In some cases a given sporangiophore bears only spor angia or sporangiola. The lateral, fertile branches arose singly, in p airs, or in verticels or pseudoverticels of three to 20. Zygospores we re described for the first time for H. pulchrum. A new genus Kirkia wa s based on H. cordense, which lacks spinelike fertile branches and has an optimal growth temperature of 25 C vs slightly below 20 C for spec ies of Helicostylum. A cladistic analysis using representative species of all sporangiate Thamnidiaceae demonstrated that Helicostylum and K irkia resided in separate clades. Selected strains of all species of H elicostylum were included in the analysis. Helicostylum venustellum wa s considered a synonym of H. pulchrum. All taxa were illustrated with line drawings. Keys were provided to genera and species, and an extens ive list of synonyms was presented.