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Name derivation:
Early (proto-) bladder (-siphon).
Classification:
Protosiphon Klebs 1886; only 1 species has been described, and it is currently accepted taxonomically (Guiry and Guiry 2014). Order Chlamydomonadales; Family Protosiphonaceae
Morphology:
Siphonous (coenocytic) unicell. Bladder-like green upper portion of cell is on soil surface (even of deserts that are occasionally dampened), non-photosynthetic lower portion is rhizoidal, anchoring it in place and absorbing NH^+4 and PO4^-2, and amino acids. Referred to as a ‘rhizophyte’ (Raven 1981). The life cycle of Protosiphon was described by Bold (1933).
Photoreversiblity:
Blue light (400 – 490 nm) inhibits, and longer wavelength light (520 – 700 nm) stimulates zoospore formation (Thomas and O’Kelly 1972).
Similar genera:
In marine habitats the unicell becomes morphologically more complex and is placed in the genus Caulerpa. Another ‘acellular’ (unicell) genus is Botrydium (Tribophyceae) that closely resembles Protosiphon on soil but doesn’t produce α-linked starch, so doesn’t stain purple with an iodine solution.
Habitat:
Terrestrial, damp soil. Capable of at least 40 years of dessication.
References:
Bold, H.C. 1933. The life history and cytology of Protosiphon botryoides. Bulletin of the Torrey Botanical Club 60(4):241-299. Guiry, M.D. and G.M. Guiry 2014. AlgaeBase. World-wide electronic publication, National University of Ireland, Galway. http://www.algaebase.org; searched on 30 May 2014. Thomas, J.P. and J.C. O’Kelley 1972. The photoreversible nature of a pigment system in the green alga Protosiphon botryoides Klebs. Photochemistry and Photobiology 17:469-472.