Octochara

Octochara is a genus of fossil charophyte (aquatic green alga) from the Famennian (Late Devonian). It is one of two genera of charophyte described from the Waterloo Farm lagerstätte in southern Africa.[1] It and Hexachara, from the same locality provide the oldest record of reconstruct able charophytes with in situ oogonia. Octochara is derived from a Greek word “octo”, meaning eight, a reference to the octoradial symmetry; chara, referring to membership of the Charales. In Octochara, a whorl of eight laterals are borne at each node. Each lateral is branched to produce four secondary branches and bears an oogonium.[2] Two species of Octochara have been described, Octochara crassa and Octochara gracilis. The two species differ in the size and the shape of their secondary branchlets and oogonia. The specific name of O. crassa is derived from Latin, “crassus”, meaning fat or thick, a reference to the branchlets. This species has whorls up to 14mm in diameter and the branchlets are relatively broad with rounded terminations. In O. crassa, the internode parts of axis are unknown at this stage but, based on measurements of the central hole through the whorls, they are estimated to be about 0.7 mm in diameter.[3] Oogonia in O. crassa are attached to the junction at which the radial branches divide and are supported within the four secondary branchlets. Each oogonium is almost spherical, about 1.7 mm long and 1.6 mm wide at widest point but tapering slightly towards the point of attachment They are helically striated in a sinistral direction with 3 5 stria visible in plan view.[4] O. crassa is differentiated from O. gracilis by the relatively greater width of its branches and branchlets which have rounded lobate, as opposed to pointed terminations. The whorls also have a larger diameter.

Octochara
Temporal range: Famennian
Partial reconstruction of Octochara crassa by Rob Gess
Scientific classification
Kingdom:
Plantae
Division:
Charophyta
Class:
Charophyceae
Order:
Charales
Family:
†Eocharaceae
Genus:
†Octochara

Gess R. W. & Hiller N., 1995
Two whorls of Octochara crassa from Waterloo Farm lagerstätte
Single whorl of Octochara gracilis (from Gess and Hiller 1995).
Reconstructions of Octochara crassa (left) and Octochara gracilis (right) from Gess and Hiller 1995.

The specific name of O. gracilis is derived from Latin, “gracills”, meaning slender, a reference to its more slender branchlets. O. gracilis comprises whorls up to 10 mm in diameter in which branchlets are narrow with slender tapering terminations. The internode portions of axis in this species appear uncorticated and vary in diameter up to 0.6 mm. In O. gracilis Chains of whorls show that whorl diameter diminishes distally. Each whorl has eight radial branches that quadrifurcate after about one-third of their length.[5] Branchlets of O. gracilis are slender with sharply pointed terminations. The oogonia are attached at the point of division of the branches and is supported within four branchlets. Each oogonium is ellipsoidal, about 1.5mm long and 0.9 mm wide at its broadest point.[6] Charophyte algae are non marine and can currently be found in lakes and less saline parts of estuaries. Likewise the charophytes at Waterloo Farm have been interpreted as being derived from less saline portions of the palaeo-estuarine environment. The charophyte algae genus is formed in less saline portions of the estuarine system.[7]

References
  1. GESS, R. W. & HILLER, N. (1995a). Late Devonian charophytes from the Witteberg Group, South Africa. Review of Palaeobotany and Palynology 89, 417–428
  2. GESS, R. W. & HILLER, N. A. (1995b). Preliminary catalogue of fossil algal, plant, arthropod, and fish remains from a Late Devonian black shale near Grahamstown, South Africa. In Annals of the Cape Provincial Museums (Natural History) (Volume 19), pp. 225–304. Cape Provincial Museums, Grahamstown, South Africa.
  3. GESS, R. W. & HILLER, N. (1995a). Late Devonian charophytes from the Witteberg Group, South Africa. Review of Palaeobotany and Palynology 89, 417–428.
  4. GESS, R. W. & HILLER, N. (1995a). Late Devonian charophytes from the Witteberg Group, South Africa. Review of Palaeobotany and Palynology 89, 417–428.
  5. GESS, R. W. & HILLER, N. A. (1995b). Preliminary catalogue of fossil algal, plant, arthropod, and fish remains from a Late Devonian black shale near Grahamstown, South Africa. In Annals of the Cape Provincial Museums (Natural History) (Volume 19), pp. 225–304. Cape Provincial Museums, Grahamstown, South Africa.
  6. GESS, R. W. & HILLER, N. (1995a). Late Devonian charophytes from the Witteberg Group, South Africa. Review of Palaeobotany and Palynology 89, 417–428.
  7. Gess, Robert W.; Whitfield, Alan K. (2020). "Estuarine fish and tetrapod evolution: Insights from a Late Devonian (Famennian) Gondwanan estuarine lake and a southern African Holocene equivalent". Biological Reviews. 95 (4): 865–888. doi:10.1111/brv.12590. PMID 32059074. S2CID 211122587.
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