Electronic Flora of South Australia Genus Fact Sheet

Genus MYRIACTULA Kuntze 1898: 74,415

Phylum Phaeophyta – Order Chordariales – Family Leathesiaceae

Thallus minute [less than 2 (–2.5) mm high], gelatinous, basally partly to slightly endophytic with a pulvinate to tufted medulla and cortex. Medulla of erect, subdichotomous, filaments 3–25 cells long, developed from basal rhizoidal filaments. Determinate cortical filaments mostly free (not forming a dense stratum), arising from upper medullary cells or directly from basal filaments, 10–40 (–80) cells long, cylindrical or with their greater diameter part way along, with phaeophycean hairs. Phaeoplasts several to numerous per cell, each usually with a pyrenoid.

Reproduction: Plurilocular sporangia borne on uppermost medullary cells forming a stratum above the medulla and at the base of the cortical filaments, clustered, mostly uniseriate. Unilocular sporangia borne on uppermost medullary cells, ovoid.

Type species: M. pulvinata (Kützing) Kuntze [=M. rivulariae (Suhr) J. Feldmann].
A genus of about 15 species (Feldmann 1943) in temperate and colder waters.

Taxonomic notes: Myriactula is morphologically similar to Elachista but differs in possessing phaeophycean hairs. It forms better defined tufts than Strepsithalia, with a distinct medulla and numerous determinate cortical filaments, but these are much less developed and less compact than in the globular thalli of Corynophlaea, and the latter genus has a basal layer on the surface of the host only, whereas the base of Myriactula is partly endophytic. The cortical filaments of

Myriactula are essentially separate and free from each other in contrast to Corynophlaea where they form a dense stratum enveloped in mucilage. Some of the following species, as for most species of Myriactula, are not well-defined and further study of species on the southern Australian coast is needed.

References:

FELDMANN, J. (1943). Une nouvelle espèce de Myriactula parasite du Gracilaria armata J. Ag. Bull. Soc. Hist. Nat. Afr. Nord 34, 222–229.

KUNTZE, O. (1898): Revisio generum plantarum vascularium. Vol. 3. (Würtzburg.)

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

Author: H.B.S. Womersley & S. Skinner

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 SPECIES OF MYRIACTULA

1. Determinate cortical filaments 16–20 (–22) µm in diameter, tapering slightly above the broadest part in their lower third; on Sargassum leaves or Hydroclathrus	M. arabica
1. Determinate cortical filaments 10–15 in diameter, cylindrical to slightly broader above; on Fucales or Scytosiphonales	2
2. Determinate cortical filaments 80–240 µ and 4–16 cells long, medulla 30–80 µm high	M. haydenii
2. Determinate cortical filaments over 500 µm and 30 cells long; medulla well developed, over 100 1.1m high in mature plants	3
3. Determinate cortical filaments 500–800 µm and 30–40 cells long; medulla becoming 100–160 µm high; on Scytosiphon	3 M. caespitosa
3. Determinate cortical filaments 500–1400 µm and 20–80 cells long; medulla well developed, 300–1000 µm high; on Cystophora monilifera	4 M. filiformis

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