Electronic Flora of South Australia Genus Fact Sheet

Genus LEPILAENA Drummond ex Harvey 1855d: 57. "Water-mats".

Phylum Magnoliophyta – Subphylum Seagrasses – Class Liliopsida – Subclass Alismatidae – Order Potamogetonales – Family Zannichelliaceae

Monoecious or dioecious; annual or perennial rhizomatous herbs. Rhizomes much-branched bearing at the nodes roots, scale leaves and erect leafy shoots. Leaves alternate, with the floral leaves often apparently sub-opposite and frequently crowded towards the apex of the stem. Sheath with ligule well developed, frequently bifid; blade linear, a single median vein and a fibrous strand on either margin. Prophylls enclosing younger organs at first, sometimes prominent. Squamules filiform, a pair at each node. Flowers inconspicuous, solitary, each flower at first enclosed in a leaf sheath. Male flower pedicellate, consisting of a single stamen with a minute cup-like perianth or 3 minute tepals; anther sessile, with 6 (2 only in L. bilocularis) pairs of microsporangia united longitudinally and dorsally, appearing at dehiscence as one six-loculed anther; pedicel at first very short, elongating considerably at anthesis to extend above the foliage. Pollen grains globose. Female flower with 3 tepals, membranous, persistent; carpels 3, free; each carpel with 1 ovule, style slender, stigma expanded, obliquely peltate or funnel-shaped. Fruit an achene.

Type species: L. australis Drummond ex Harvey.

Taxonomic notes: A genus of four or more species confined to Australasia, mainly in fresh or brackish water. Two species are marine in southern Australia.

Species of Lepilaena tolerate a wide range of salinity from fresh water through brackish water to salinities exceeding those of seawater. They occur in both temporary and permanent inland waters, in salt lakes and estuaries and also sometimes in truly marine habitats subject to tidal influences. The marine species commonly found around the southern Australian coast is a previously undescribed species (L. marina, see below).

Tomlinson (1982, p. 339) discusses the stamen of Lepilaena, which has been variously interpreted by different workers. He describes it as having 6 units (2 only in L. bilocularis), with each unit or pollen sac consisting of a pair of microsporangia, i.e. a total of 12 microsporangia. These are clearly seen in the cross section of the young stamen (Fig. 20K). The wall separating the 2 microsporangia within the pollen sac breaks down at maturity leaving a single locule in each pollen sac, i.e. a total of 6 locules from which the pollen grains are released.

References:

HARVEY, W.H. (1855d). Characters of some New Genera of plants recently discovered by Mr James Drummond in Western Australia. J. Bot. Kew Gard. Misc. (ed. J.D. Hooker) 7, 51–58. Harvey, W.H. (1857). List of Dr Harvey's duplicate Australian algae.

TOMLINSON, P.B. (1982). Helobiae (Alismatidae) including the seagrasses. Vol. VII. Anatomy of the Monocotyledons (ed. C.R. Metcalfe). (Clarendon Press: Oxford.)

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

Author: H.B.S. Womersley

Publication: Womersley, H.B.S. (31 May, 1984)
The Marine Benthic Flora of Southern Australia
Part I
©Board of the Botanic Gardens and State Herbarium, Government of South Australia

KEY TO SPECIES OF LEPILAENA

1. Mature fruit L/B usually 3–4 (–6), fruit longer than the tepals and projecting beyond them; pedicel elongating after fertilisation, fruits extending well beyond the leaf sheath. 1

L. cylindrocarpa

1. Mature fruit L/B usually 1.5–2.5 (–3), fruit shorter than the tepals and remaining enclosed within them; pedicel remaining short, fruits usually not extending beyond the leaf sheath

2

2. Plants monoecious; leaf blade 0.1–0.2 mm broad, apex tapering to an acute or acuminate tip; female flowers borne singly but clustered together with male flowers in groups in the leaf sheaths

L. preissii*

2. Plants dioecious; leaf blade 0.2–0.4 (–0.5) mm broad, apex usually truncate with a central mucro; female flowers axillary, borne singly and appearing solitary

L. marina sp. nov.


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