The genus Posidonia König (nom. cons.) (Posidoniaceae).




Author:

C.D.E. König (1805) In: König, C.D.E. and Sims, J. Ann. Bot. 2:95, t.6

Species:

Nine species of Posidonia are currently recognised, of which eight are found in Australia. All eight Australian species occur in Western Australia. Kuo and McComb (1989) separate the species into two major groups, the P. australis group and the P. ostenfeldii group.

Recent studies on the genetic relationships between Posidonia robertsoniae and Posidonia coriacea have suggested that there are few grounds to support the existence of five species within the Posidonia ostenfeldii complex (Kendrick et al., 1997). In particular, the study suggested that the differences between Posidonia robertsoniae and P. coriacea may be largely the result of environmental and developmental factors, and that there is little evidence to support two different species.

Life history

Posidonia plants are monoecious. The inflorescences comprise several spikes terminating on a leafless stem. Each spike has two bracts reducing in size with height, and bears between three and six (varies with species) hermophrodytic flowers. Flowering occurs in late winter to early spring, with ripe fruit evident in early to mid summer. The fruit float due to air spaces within the pericarp. With the disintegration of the pericarp the seed falls out, sinks and begins germinating immediately (den Hartog, 1970; Aston, 1973).

Distribution

The eight Australian species of Posidonia are all found in Western Australia. P. angustifolia, P. coriacea, P. denhartogii and P. sinuosa are additionally found in South Australia, and P. australis occurs in New South Wales, South Australia, Tasmania, Victoria and Western Australia.

Posidonia australis group


Posidonia angustifolia - click for a larger image (26.5 kb)

Posidonia angustifolia Cambridge and Kuo


(Cambridge, M.L. and Kuo, J. (1979) "Two new species of seagrasses from Australia, Posidonia sinuosa and P. angustifolia (Posidoniaceae)" Aquatic Botany 6:312, figs. 3, 6, 9, 15, 17, 19, 20b.)

Distribution and ecology:

Cambridge and Kuo (1979) list the range of P. angustifolia from the Houtman Abrolhos, and along the south-west coast of Western Australia to Encounter Bay, South Australia. Robertson (1984) listed an extended range as far east as Port MacDonnell near the Victorian border, and Walker (1990) reported this species as far north as Shark Bay.

This species is found sublittorally at depths of from 2 to 35 m on substrates of fine sand with larger sized fractions. P. angustifolia occurs most frequently in open inshore waters; while reported as a meadow-forming species (Kirkman and Kuo, 1996), it is frequently found together with other seagrass species, particularly in its deeper range (Robertson, 1984). Robertson also noted that some plants from the eastern limit of its range are of a broad-leaved form, and may be intermediate between P. angustifolia and P. australis.



Posidonia australis - click for a larger image (26.5 kb)

Posidonia australis J.D. Hook.


(Hooker, J.D. (1858) Flora Tasmaniae Vol. 2:43)


Posidonia sinuosa Cambridge and Kuo

(Cambridge, M.L. and Kuo, J. (1979) "Two new species of seagrasses from Australia, Posidonia sinuosa and P. angustifolia (Posidoniaceae)" Aquatic Botany 6:312, figs. 3, 6, 9, 15, 17, 19, 20b.)

Posidonia ostenfeldii group

Posidonia coriacea Cambridge and Kuo

(Cambridge, M.L. and Kuo, J. (1979) "Two new species of seagrasses from Australia, Posidonia sinuosa and P. angustifolia (Posidoniaceae)" Aquatic Botany 6:312, figs. 3, 6, 9, 15, 17, 19, 20b.)


Posidonia denhartogii Kuo and Cambridge

Kuo, J. and Cambridge, M.L. (1984) A taxonomic study of the Posidonia ostenfeldii complex (Posidoniaceae) with descriptions of four new Australian seagrasses. Aquat. Bot. 20, 267-95.


Posidonia kirkmanii Kuo and Cambridge

Kuo, J. and Cambridge, M.L. (1984) A taxonomic study of the Posidonia ostenfeldii complex (Posidoniaceae) with descriptions of four new Australian seagrasses. Aquat. Bot. 20, 267-95.


Posidonia ostenfeldii den Hartog

den Hartog, C. (1970) Seagrasses of the World. Verh. Kon. Ned. Akad. Wetens. Afd. Naturk. Ser. 2 59:139


Posidonia robertsonae Kuo and Cambridge

Kuo, J. and Cambridge, M.L. (1984) A taxonomic study of the Posidonia ostenfeldii complex (Posidoniaceae) with descriptions of four new Australian seagrasses. Aquat. Bot. 20, 267-95.


The Western Australian Seagrass Web pages were created and are maintained by:

Mike van Keulen
Murdoch University
Western Australia.
Last update: Tuesday, 25 October, 2005 10:14