Electronic Flora of South Australia Family Fact Sheet

FAMILY LEATHESIACEAE Farlow

Phylum Phaeophyta – Order Chordariales

Thallus of small, usually compact, tufts to a few mm high, or globose, or pulvinate and lobed, epiphytic or epilithic, with the medullary and usually the cortical filaments embedded in a gelatinous matrix. Basal layer of filaments, often irregular, partly endophytic in some epiphytic taxa. Medulla of erect, branched, colourless cells, slightly to extensively developed, bearing a well defined cortex of determinate assimilatory filaments together with phaeophycean hairs; in one genus, phaeophycean hairs present as apical continuations of cortical filaments. Cells with few to numerous phaeoplasts each usually with a pyrenoid. Growth of medullary and cortical filaments intercalary or subapical. Microthallus microscopic, filamentous, with uniseriate gametangia.

Reproduction: Reproduction by essentially uniseriate plurilocular sporangia and ovoid unilocular sporangia, borne on upper medullary filaments and lying within the cortex; the gametophyte by plurilocular gametangia where known.

A family of about 8 genera, ranging from the small tufts of Strepsithalia to the relatively large, gelatinous cushions of Leathesia. The Leathesiaceae differ from the Elachistaceae in the presence of phaeophycean hairs, and usually the whole thallus (except the hairs) is embedded in mucilage; the determinate cortical filaments are of similar height within a thallus (and species) and usually form a distinctive layer. The simplest member, Strepsithalia, is similar in form to some ectocarpaceous genera (e.g. Streblonema), but differs in having more defined tufts which are more mucilaginous, a better defined stratum of determinate cortical filaments, and uniseriate plurilocular sporangia (present in some species of Streblonema). The relationships between these two genera need further study.

Life history probably diplohaplontic and heteromorphic (Dangeard 1969, p. 80).

References:

DANGEARD, P. (1969). A propos des travaux récents sur le cycle evolutif de quelques Phéophycées, Phéosporées. Botaniste 52, 59–102.

The Marine Benthic Flora of Southern Australia Part II complete list of references.

Author: H.B.S. Womersley

Publication: Womersley, H.B.S. (14 December, 1987)
The Marine Benthic Flora of Southern Australia
Part II
©Board of the Botanic Gardens and State Herbarium, Government of South Australia

KEY TO GENERA OF LEATHESIACEAE

1. Thallus of small epiphytic tufts, or spreading, less than 2 mm high, with or without an endophytic base; medullary filaments a few to many cells long, with determinate cortical filaments present in clusters or singly, free but of uniform height within a species; phaeophycean hairs produced from medullary cells or as continuations of the cortical filaments

2

1. Thallus 2–40 (–80) mm across and 2–20 mm thick, globular to pulvinate or lobed, compact, mucoid, epiphytic or epilithic; medulla well developed; cortical filaments closely associated laterally and forming a distinct stratum embedded in mucilage; phaeophycean hairs produced from medullary cells

4

2. Thallus of minute tufts, or spreading, with prostrate, endophytic filaments and only slight development of erect medullary filaments, bearing frequent (but rarely densely tufted) determinate cortical filaments and phaeophycean hairs, together with single or small groups of plurilocular sporangia and/or unilocular sporangia

STREPSITHALIA

2. Thallus usually of well defined globular or hemispherical tufts, with a distinct medulla three to many cells high giving rise to numerous determinate cortical filaments (largely or partly free of mucilage), and with clusters of plurilocular (or unilocular) sporangia arising from upper medullary cells

3

3. Phaeophycean hairs formed as apical continuations of some determinate cortical filaments; thallus epiphytic

ACROTRICHIUM

3. Phaeophycean hairs formed laterally from upper medullary cells; thallus basally endophytic

MYRIACTULA

4. Determinate cortical filaments 10–60 cells long, unbranched, usually curved above and with laterally swollen cells; epiphytic

CORYNOPHLAEA

4. Determinate cortical filaments 4–10 cells long, simple or branched; epilithic or epiphytic

5

5. Determinate cortical filaments branched, cylindrical; medullary cell anastomoses absent; unilocular sporangia often laterally attached; epilithic

PETROSPONGIUM

5. Determinate cortical filaments simple, with an inflated terminal cell; medullary cells anastomosing; unilocular sporangia basally attached; epilithic or epiphytic

LEATHESIA


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