Home / Anomalous_Items / Aquatic_Macrophytes / Emergent_Leaves / Hippuris
Click on images for larger format
Name derivation:
Hippus (Gk) – horse, urus – tail Common name ‘mare’s tail’
Classification:
Hippuris Linneaus;only 1 – 3 species descriptions are currently accepted taxonomically. Order Lamiales; Family Plantaginaceae (earlier Hippuridaceae Dicot
Morphology:
Extend 20-30 cm above water surface. Leaves are arranged in whorls of 6-12, each leaf up to 3 mm wide and 2.5 cm long.  The leaf number per whorl increases continuously with increasing size of the apical meristem (Rutishauser 1999). Flowers, inconspicuous without sepals and petals, are sessile, located singly in axils of whorled leaves. Rhizomatous, with roots that transmit methane to leaves and then atmosphere from anoxic organic sediments. Fruits are achenes 2 mm long. High-altitude H. montana is smaller (10 cm tall) with shorter leaves than H. vulgaris. In spaceflight tests with microgravity Hippurus had reduced PAL (phenylalanine ammonia-lyase) activity by 28 – 37% (Nedukha 1997).
Similar genera:
Superficially can be misidentified as an Equisetum ‘horsetail’ (non-flowering) or Myriophyllum spp.
Habitat:
Freshwater, shallow areas of lakeshore and rivers. North and South America, Australia, Eurasia. Range extends into arctic lakes including coastal Greenland and (unconfirmed) coastal Antarctica (Camp 1947). At higher elevation H. Montana is more terrestrial in damp sites. Seeds and leaves eaten by wildlife.
References:
Camp, W.H. 1947. Distribution patterns in modern plajnts and the problems of ancidnt dispersal. Ecological Monographs 17(2):159-193. Nedukha, E.M. 1997. Effects of microgravity on the structure and function of plant cell walls. International Review of Cytology 170:39-77. Rutishauser, R.  1999.  Polymerous leaf whorls in vascular plants:  Developmental morphology and fuzziness of organ identities.  International Journal of Plant Sciences 160(S6):S81-S103.