Vegetative and reproductive morphology of Hummbrella hydra Earle (Rhodophyta, Gigartinales)

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Abstract
Pseudoanemonia tentacula Chapman from New Zealand is synonymized with Hummbrella hydra Earle from Chile. Morphologically Hummbrella resembles the ‘Batrachospermum-type’ construction in several respects. The thallus consists of a cylindrical stipe with an array of branches (arms) at its apex. Only gametophytes have been encountered in the field. Thalli are monoecious. Spermatangia form on the epidermal cell layer of the thallus arms. Hummbrella is monocarpogonial and procarpic. The three-celled carpogonial branch becomes four-celled following a presumed fertilization and division of the carpogonium. The supporting cell is intercalary in a normal vegetative filament and functions as the generative auxiliary cell. Indirect evidence suggests that the fourth post-carpogonial branch cell cuts off a small initial containing the diploid nucleus and this fuses directly with the auxiliary cell. A single gonimoblast initial is produced from the auxiliary cell and grows thallus outwards developing a lobed carposporophyte most cells of which form carpospores. The carposporophyte is surrounded by involucral branches. In its combination of vegetative and reproductive morphology Hummbrella hydra is unique among Rhodophyta. It is placed in the Gigartinales in the monotypic family Pseudoanemoniaceae.