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MORPHOLOGY AND TAXONOMY OF HIMANTOTHALLUS (INCLUDING PHAEOGLOSSUM AND PHYLLOGIGAS ), AN ANTARCTIC MEMBER OF THE DESMARESTIALES (PHAEOPHYCEAE) 1
Author(s) -
Moe Richard L.,
Silva Paul C.
Publication year - 1981
Publication title -
journal of phycology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.85
H-Index - 127
eISSN - 1529-8817
pISSN - 0022-3646
DOI - 10.1111/j.1529-8817.1981.tb00814.x
Subject(s) - stipe (mycology) , biology , sporangium , botany , holdfast , thallus , plasmodesma , anatomy , tendril , ultrastructure , spore
The sporophyte of Himantothallus develops according to a closed pattern in which the number and position of the blades is determined by the location of trichothallic meristems in a filamentous germling. Expansion of the miniature juvenile to the massive adult thallus is accomplished by diffuse secondary growth and involves a change from filamentous rhizoids to a hapteroid holdfast, flattening of the stipe, and enormous increases in length, breadth, and thickness of both stipe and blade. The axis usually bears 1–8 lateral blades, often paired, and terminates in a flattened stub. Phaeoglossum is interpreted as a growth form of Himantothallus in which a terminal blade develops to the exclusion of lateral blades, the latter being represented by a single spine. Phyllogigas clearly falls within the morphological spectrum of Himantothallus , the lack of twisting being related to physical factors in the environment. Sporangia, interspersed with an equal or somewhat larger number of two‐celled paraphyses, are borne in slightly elevated sori scattered over both surfaces of the blade. Zoospore germination was not observed, nor were gametophytes, either in culture or in the field. Haptera apparently originate from the meristoderm in the lower part of the maturing stipe and lack a filamentous medulla. The mature stipe and the mature blade are anatomically similar, being composed of a superficial meristoderm, a cortex of parenchyma‐like cells, and a filamentous medulla. The meristoderm is usually a single layer of plastid‐containing cells that divide anticlinally to accommodate (or effect) expansion and periclinally to produce cortical tissue inward. Cortical cells are in radial files and increase in diameter towards the interior. They usually are densely packed with physodes. The medulla is uniquely distinguished by the presence of sheathed trumpet hyphae. Cells of the trumpet hyphae have perforate end walls with callose deposits and probably function in conduction as do the sieve filaments in Laminariales. Sheathing cells are filled with plastids. Sheathing filaments form connections among themselves and with nearby unsheathed filaments. The sheathed trumpet hyphae and their matrix of unsheathed filaments form a plexus, which in the mature blade is flattened and may be stripped intact from the other tissues. Development of the embryonic sporophyte is very similar to that in Desmarestia , as is the anatomy of the adult thallus and the sporangia. From these considerations, Himantothallus is assigned to the Desmarestiaceae (Desmarestiales).