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Halodule beaudettei

(Shoal-Grass)

Common Names

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Common Names in English:

Shoal-Grass, Shoalweed

Description

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Family Cymodoceaceae

Herbs, perennial , rhizomatous , caulescent ; turions absent. Leaves submersed , alternate or nearly opposite, sessile; sheath persisting longer than blade , leaving circular scar when shed, not ligulate , auriculate , lobes not scarious ; blade linear; intravaginal squamules scales , more than 2. Inflorescences axillary or terminal , solitary or cymes, without spathe , sessile or pedunculate ; peduncle, when present, not elongating following fertilization, not spiraling. Flowers uniasexual, staminate and pistillate on separate plants ; subtending bracts absent; perianth absent. Staminate flowers : stamens 2, in 1 series; anthers adaxially connate , dehiscing vertically; pollen linear . Pistillate flowers: pistils 2, distinct , not stipitate ; ovules pendulous, orthotropous . Fruits achenelike or drupaceous . Seeds 1; embryo straight.

Genera 5, species 16 (2 genera, 2 species in the flora ) : widespread in warm oceanic waters worldwide.

Cymodoceaceae comprise one of three families of flowering plants in North America that inhabit oceanic waters. Individuals of this family form carpetlike vegetation over sandy to muddy substrates of the tropical and subtropical waters along the southern Atlantic and Gulf of Mexico coasts of the United States.[1]

Genus Halodule

Stems erect , subtended by elliptic or ovate scales . Leaves 1--4; blade flattened, apex 2--3-toothed, lacunae absent; veins 3, midvein conspicuous , widened distally, lateral veins inconspicuous, each ending in tooth . Inflorescences solitary. Flowers axillary to leafy bract, inflated sheath absent. Staminate flowers : anthers attached to axis at different levels. Pistillate flowers nearly sessile, styles not divided into stigmas. Fruits achenelike, slightly compressed , nearly globose to ovoid .

Species 6: warm oceanic waters of both hemispheres.

The taxonomy of Halodule is based almost entirely on the shape of the vegetative leaf tip ; many of the species are unknown in sexual reproductive condition. Features of the leaf tip important in systematics include the presence or absence of lateral teeth , the presence or absence of a middle tooth, and the length of the middle tooth relative to the two lateral ones.

For a discussion of pollination in Halodule pinifolia (Miki) Hartog, see P. A. Cox (1988) and P. A. Cox and R. B . Knox (1989). The flowers are enclosed in a vegetative shoot that closely resembles a perianth (E. A. Johnson and S. L. Williams 1982). Staminate flowers are borne at the surface of the substrate, and pistillate flowers are produced below the substrate (P. A. Cox 1988). During low tide , the filament elongates , projecting the anther to the water surface. Following exposure to air , the anthers dehisce , releasing a cottony-like mass of threadlike pollen grains approximately 1000 m m in length. These pollen grains rapidly assemble themselves into "search vehicles" that are relatively large, ca. 5000 m m. This large size apparently increases the possibility of contacting a stigma. Apparently most search vehicles are composed of pollen from one anther. Submarine dehiscence does occur (P. A. Cox 1988) ; no explanation is given for what occurs afterwards.

The pistillate flower is produced below the soil surface (P. A. Cox 1988). The elongate style projects the stigma to the water surface during low tide. Possibly a relatively large "search vehicle" floating on the water surface will contact a stigma and pollination is accomplished. The fruit develops in the substrate, remaining there until released from the plant. Fruits remaining in the substrate possibly are the reason so few collections have fruits on them. They could fall off during the collection and removal of the substrate.[2]

Taxonomy

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Notes

Publishing author : Hartog Publication : Blumea 12: 303 1964 Basionym author: (Hartog)Place of publication: Blumea 12:303. 1964

Name verified on 05-Nov-1999 by ARS Systematic Botanists.

Similar Species

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Members of the genus Halodule

ZipcodeZoo has pages for 13 species, subspecies, varieties, forms, and cultivars in this genus:

H. australis · H. beaudettei (Shoal-Grass) · H. bermudensis · H. brasiliensis · H. ciliata · H. emarginata · H. lilianeae · H. pinifolia · H. tridentata · H. uninervis (Narrowleaf Seagrass) · H. univervis · H. wrighti · H. wrightii (Shoal-Grass)

More Info

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Further Reading

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Notes

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Contributors

Identifiers

Footnotes

  1. Robert R. Haynes "Cymodoceaceae". in Flora of North America Vol. 22. Oxford University Press. Online at EFloras.org. [back]
  2. "Halodule". in Flora of North America Vol. 22. Oxford University Press. Online at EFloras.org. [back]
Last Revised: 7/1/2009