Search

The only known population ofBatrachospermum spermatiophorumVisetSheath, located in a small stream on east Maui, Hawaii, was sampled from November 2001 to October 2002 to investigate its phenology. Additionally, the taxonomic status of the alga was examined. Phylo­genetic analyses of the large subunit of the ribulose-1,5-bisphosphate carboxylase/oxygenase (rbcL) gene forB. spermatiophorumconfirm its placement within the SectionContortaof the genusBatrachospermum. Comparisons withrbcL gene sequences for all other availableBatrachospermumspecies, including 10 other members of the SectionContorta, illustrate thatB. spermatiophorumis distinct in itsrbcL nucleotide sequence and should be maintained as a separate species. The phenology ofB. spermatiophorumdiffered from most studies ofBatrachospermumreproduction in that the gametophytes were present year round, and no macroscopic chantransia stages were identified at any point during the present study. Maximum plant length was highest in the late fall and early winter months, while gametangial production peaked in February and March. Carposporophyte abundance rose sharply in July and August, and the percentage of carposporophytes producing carpospores was highest in late summer and early fall months. Although significant correlations were determined among stream conditions and among phenological characteristics, only pH was associated with several of the reproductive characters, which is unusual for studies ofBatrachospermumphenology. Timing of sexual reproduction for all macroalgal community members in the stream site was not coordinated, with some reproducing year round and others more sporadically. The year-round presence ofBatrachospermumgametophytes may be a result of a combination of smaller seasonal changes in cues such as day length and water temperature in the tropical environment than occur in temperate locations, and lack of extreme conditions that might inhibit the persistence of the gametophyte. [ABSTRACT FROM AUTHOR]

SUMMARYThe development and release of the unique vegetative propagules of the freshwater encrusting alga Hildenbrandia angolensis Welwitsch ex West et West, gemmae, were studied using several different microscopic and histochemical techniques. In addition, the seasonality of gemma production was monitored bimonthly over a 12-month period in two spring-fed streams in Texas, USA. Gemmae differentiate within the thallus and are subsequently released from the surface of the crust. Release of the gemmae most likely occurs by digestion of surrounding cells, as suggested by the presence of starch granules and lipid globules in the region between the released gemma and the thallus. The initial separation of the gemmae from the thallus occurs from the sides of the gemma or the bottom, or possibly simultaneously. Contrary to previous studies, we have observed that gemma production occurs endogenously within the thallus of freshwater Hildenbrandia, rather than on the surface of the crust in raised structures. Histochemical tests and electron microscopic examination indicate that the cells of the gemmae contain a large amount of floridean starch. The starch granules frequently form rings surrounding the nuclei of both gemma and thallus cells; a feature infrequently reported for florideophyte red algae. Our seasonality investigations indicate that large fluctuations in gemma production occur over 1 year, but at least some gemma production continues year-round in the streams examined. [ABSTRACT FROM AUTHOR]