Electronic Flora of South Australia Family Fact Sheet

FAMILY LESSONIACEAE Setchell & Gardner

Phylum Phaeophyta – Order Laminariales

Thallus (sporophyte) erect or with more or less erect fronds arising from a prostrate holdfast, much divided. Holdfast much branched, with terete or compressed, robust, haptera arising from the base of the stipes. Fronds arising by splitting in the transition region when young, in some genera (Macrocystis) with laterals arising from the apex of long fronds. Laterals (blades) simple, ligulate, flat, usually with a spinous margin, often longitudinally corrugate, with or without pneumatocysts. Structure with a relatively broad, central, medulla of filaments and hyphae, including some sieve-tube like elements (especially in the stipes), and an outer small-celled cortex with a surface meristoderm which continues activity at margins of blades and in pneumatocysts and stipes.

Gametophytes microscopic, filamentous, dioecious, the female less branched and with larger cells than the male.

Reproduction: Reproduction of the sporophyte involving surface sori of unilocular sporangia (with paraphyses) on blades close to the holdfast. Gametophytes oogamous.

Taxonomic notes: A family of some 8 genera, including some of the longest of all algae (e.g. Macrocystis, Nereocystis), particularly well developed on the Pacific coast of North America. In southern Australia two genera occur.

References: The Marine Benthic Flora of Southern Australia Part II

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 LESSONIACEAE

1. Thallus with a prostrate stoloniferous holdfast with short stipes and simple, ligulate, longitudinally corrugate blades 0.5–2 m long

LESSONIA

1. Thallus with a much branched holdfast of haptera, producing many erect fronds with long terete stipes bearing ligulate, smooth to corrugate, blades essentially on one side of the stipe, and each with a basal pneumatocyst

MACROCYSTIS


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