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Reproductive structures and seasonality of Dictyopteris latiuscula (Dictyotales, Phaeophyceae) from the pacific coast of Japan
Abstract
Reproductive structures of Dictyopteris latiuscula from the Pacific coast of Kanto, Japan and reproductive seasonality in Shimoda, Shizuoka Pref. were studied. This is the first report of female gametophytes and oogonia of the species. Mature sporophytes and gametophytes were simultaneously collected in late spring to early summer. Reproductive season of the species was differed between Chiba and Shizuoka.
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Tetrasporophytes and female and male gametophytes of Dictyopteris prolifera (Okamura) Okamura (Dictyotales, Phaeophyceae) were collected in Pacific coast of Japan. This is the first report of the male gametophyte from field collections. Tetrasporangial sori and gametangial sori are produced on both sides of blades. Tetrasporangial sori develop in belts along both sides of the midrib. Male and female gametangial sori are scattered on both sides of the midrib. With the further maturation, tetrasporangial sori and male and female gametangial sori sometimes extend toward the midrib. Tetrasporangia are spherical or elliptical, project above the cortex, and have 1-4 stalk cells at the base. In a tetrasporangial sorus, sporangia in various stages of development are randomly arranged. Oogonia are spherical, obovoid or ellipsoidal, and have a stalk cell at the base. In an oogonial sorus, oogonia at almost the same developmental stage are clustered close together with no space between them. This is the first description within Dictyopteris of the tightly aggregated oogonial arrangement. Antheridial sori project above the cortex, and are surrounded by 2-5 rows of immature antheridial cells. An antheridium has 1-2 stalk cells at the base.
Detailed studies on the sporophytes and gametophytes of Dictyopteris australis and Dictyopteris muelleri from Australia have demonstrated the usefulness of several reproductive characters in species discrimination. In D. australis, spherical sporangia that project above the thallus surface and are clustered around reflexed bundles of paraphyses contrast markedly with the angular sporangia of D. muelleri, which are embedded in the thallus and are scattered in broad fertile zones on the upper branches. In D. muelleri, tetrads of released spores enveloped by the inner sporangial wall are temporarily retained above the thallus surface on the ends of mucilaginous stalks. Sporangial stalks have not been reported in any other species of the brown algae, although egg stalks are produced by several fucalean species. Differences in oogonial structure can also be used to distinguish D. australis and D. muelleri. The spherical oogonia of D. australis, which project above the thallus surface, are conspicuously different from the angular embedded oogonia of D. muelleri. Detailed comparative studies on other species of Dictyopteris are now required to ensure that reproductive characters are used not only to define species of Dictyopteris but also to effectively circumscribe the genus.
Taxonomic re-examination of Dictyopteris punctata Noda revealed vegetative and reproductive characters that were not described in the original description. The outer one-fifth to two-fifths of the blade margin was monostromatic. Reproductive organs of female and male gametophytes were observed for the first time. All reproductive organs (sporangia, oogonia, antheridia) were formed on middle to upper parts of thalli and between the midrib and distromatic area of the blades, and never produced on the monostromatic areas. Maturation starts earlier at the lower part. Sporangia were solitary and scattered. Oogonia were scattered singly or in small groups and more densely distributed than sporangia. Antheridial sori were scattered around a midrib, and raised above the wing surfaces. Antheridia were taller around the midrib than in the middle part of a wing. The monostromatic wings and lack of distinct oogonial sori are new taxonomic characters of Dictyopteris punctata and further define this species with scattered sporangia, the taxonomic character hitherto used.