Variations in Cystocarp Structure in Pterocladia (Gelidiales: Rhodophyta)

Abstract

Unilocular cystocarps distinguish Pterocladia from the morphologically similar Gelidium, which exhibits bilocular cystocarps. Unequally developed locules, regarded as exceptional, have been found in two species assigned to Pterocladia. This study describes the patterns of morphological variation found during cystocarpic development in Pterocladia musciformis Taylor and in P. capillacea (Gmelin) Bornet & Thuret. About 70% of the cystocarps of P. musciformis are Gelidium-type. The remaining exhibit unequally developed locules with a longitudinal septum displaced off-center, sometimes producing spores on only one side of the cystocarp and with one or a few ostioles only on the most protruding face of the frond or blade. In a Brazilian population of Pterocladia capillacea the internal cystocarpic structure changes with age. Young cystocarps exhibit the typical structure of the genus. In more mature cystocarps the septum is located close to the middle of the cystocarp, splitting the cavity, which then appears as two unequallocules. A few ofthese larger cystocarps show pericarps protruding equally on both surfaces of the frond and with ostioles on each surface. It is concluded that the origin of the placenta seems to be the only consistent reproductive difference that distinguishes Gelidium from Pterocladia. It spite of the comparative scarcity of gametophytes, this distinction is the only important one. Under this concept, the new combination Gelidium musciforme is proposed. The pattern of cystocarpic development exhibited by Pterocladia capillacea is clearly different from the one shown by P. lucida (R. Brown) J. Agardh, the type species of the genus. However, additional studies of interspecific and intraspecific variation in cystocarpic development in the genera Pterocladia and Gelidium seem desirable before erecting a new genus.