EFFECT OF ANATOMICAL STRUCTURE ON THE BUOYANCY OF ACHENES OF 2 SUBSPECIES OF BOLBOSCHOENUS-MARITIMUS

Differences between two subspecies of Bolboschoenus maritimus (L.) PAL LA (= Scirpus maritimus L.) in different habitats (liberal and terrest rial) are partly due to variations in the buoyancy of their achenes, c aused by different anatomical structure of the fruits. This hypothesis was tested by comparing fruit buoyancy and anatomy of both subspecies at several localities. Plants were sampled from Bolboschoenus maritim us subsp. maritimus (plants with branched inflorescences and triangula r fruits, 4 localities) and B. maritimus subsp. compactus (HOFFM.) HEI NY (plants with compact inflorescences and prevailing concave fruits, 4 localities) in the Czech and Slovak Republics, and B. maritimus subs p. compactus (plants with compact inflorescences and convex fruits, 1 locality) from the coast of South Sweden. From each locality a plant w ith several tubers connected by rhizomes was taken and transferred int o the experimental garden; from these cultivated plants (clones) mixed samples of fruits collected from each clone were used for buoyancy te sts and a study of their anatomy. Fruit buoyancy was found to depend o n the anatomical structure of the pericarp - the presence of aeriferou s tissue in the exocarp serves as the main floating organ. This differ entiated all plants studied into two groups: short-floating subsp. mar itimus, with a thin or none aeriferous tissue in the exocarp, and long -floating subsp. compactus with well developed aeriferous tissue. Diff erences in fruit buoyancy corresponds to differences in the prevailing habitat types of both subspecies studied in the inland sites: the fre quent occurrence of subsp. compactus in temporarily flooded terrestria l habitats contrasts with the prevalence of subsp. maritimus in the li ttoral of water bodies. This is an example of intra-specific ecologica l differentiation leading to differentiation in wetland communities.