Rhodaphanes brevistipitata gen. et sp nov., a new member of the Stylonematophyceae (Rhodophyta)

Rhodaphanes brevistipitata gen. and sp. nov. was isolated into culture as an epiphyte on the red alga Spermothamnion cymosum from a collection made at Point Lonsdale, Victoria, Australia. It is morphologically and cytologically very similar to Stylonema species. It is short (< 1.2 mm), clavate, uniseriate to multiseriate, usually unbranched and with a short stipe. Each cell has one purple-grey multilobed plastid with a central pyrenoid and peripheral nucleus. Reproduction is by release of vegetative cells (archeospores) individually or when the whole thallus gelatinises. Free spores observed in time-lapse videomicroscopy are round (7-12 mu m) and glide without substratum contact. Molecular analysis of a partial sequence of the nuclear-encoded small subunit ribosomal RNA gene and plastid encoded photosystem If reaction centre protein D1 (psbA) placed Rhodaphanes in the Stylonematales, but more closely related to the genera Bangiopsis and Purpureofilum than to Stylonema. Ultrastructural examination of archeospores revealed a rough endoplasmic reticulum (RER) - Golgi association typical of the Stylonematophyceae and plastids lacking a peripheral limiting thylakoid, a feature not seen in any other genus of the class. The low-molecular weight carbohydrates digeneaside, sorbitol and trehalose are present.