Oligarrhena R.Br.
Prodr. 549 (1810)

Name Status: Current
Browse to the list of specimens for Oligarrhena R.Br.

Scientific Description
H.R. Coleman, Thursday 8 September 2016

Family Epacridaceae.

Habit and leaf form. Shrubs; evergreen; leptocaul, or pachycaul. Helophytic to xerophytic. Leaves minute; alternate; spiral, or four-ranked; ‘herbaceous’, or leathery; imbricate; sessile; non-sheathing; simple. Leaf blades entire; flat; parallel-veined; cross-venulate, or without cross-venules. Leaves without stipules. Leaf blade margins flat. Stem anatomy. Nodes unilacunar. Secondary thickening developing from a conventional cambial ring.

Reproductive type, pollination. Fertile flowers hermaphrodite. Unisexual flowers absent. Plants hermaphrodite. Entomophilous, or ornithophilous. Pollination mechanism unspecialized.

Inflorescence and flower features. Flowers aggregated in ‘inflorescences’; in spikes. Inflorescences compound (the numerous small spikes forming a leafy raceme); axillary. Flowers bracteate; bi- bracteolate; minute; fragrant, or odourless; laterally compressed; 4 merous; cyclic; tetracyclic. Free hypanthium absent. Hypogynous disk present; intrastaminal; of separate members (4 distinct scales). Perianth with distinct calyx and corolla; 8; 2 -whorled; isomerous. Calyx 4; 1 -whorled; polysepalous; imbricate; exceeded by the corolla; regular; persistent. Corolla 4; 1 -whorled; gamopetalous; lobed. Corolla lobes about the same length as the tube. Corolla valvate; campanulate; regular; glabrous abaxially; glabrous adaxially; white, or yellow; persistent, or deciduous. Androecium 2, or 4. Androecial members adnate (to the corolla); all equal; free of one another; 1 -whorled. Androecium exclusively of fertile stamens, or including staminodes. Staminodes when present, 2; representing the alternate deficient members. Stamens 2. Staminal insertion in the throat of the corolla tube. Stamens remaining included; reduced in number relative to the adjacent perianth; oppositisepalous; all alternating with the corolla members. Filaments glabrous; filiform (very short). Anthers basifixed, or adnate; becoming inverted during development, their morphological bases ostensibly apical in the mature stamens; non-versatile; dehiscing via longitudinal slits (by a single median slit); finally introrse (inverting during development); unilocular, or bilocular; bisporangiate; unappendaged. Pollen shed as single grains; without viscin strands. Gynoecium 2 carpelled. The pistil 2 celled. Gynoecium syncarpous; eu-syncarpous; superior. Ovary plurilocular; 2 locular. Gynoecium stylate. Styles 1; very short; attenuate from the ovary; apical. Stigmas 1; minute, truncate, or clavate, or capitate. Placentation axile. Ovules 1 per locule; pendulous; non-arillate; anatropous.

Fruit and seed features. Fruit fleshy, or non-fleshy; indehiscent; a drupe (small). The drupes with one stone. Fruit 1 seeded. Seeds endospermic. Endosperm oily. Seeds wingless. Embryo well differentiated. Cotyledons 2. Embryo straight. Seedling. Germination phanerocotylar.

Physiology, biochemistry. Aluminium accumulation not found. Photosynthetic pathway: C3.

Geography, cytology, number of species. Native of Australia. Endemic to Australia. Australian states and territories: Western Australia. South-West Botanical Province.

Additional characters Prophylls few. Corolla lobes erect.

Taxonomic Literature

  • Wheeler, Judy; Marchant, Neville; Lewington, Margaret; Graham, Lorraine (2002). Flora of the south west, Bunbury, Augusta, Denmark. Volume 2, dicotyledons. Australian Biological Resources Study. Canberra.
  • Blackall, William E.; Grieve, Brian J. (1981). How to know Western Australian wildflowers : a key to the flora of the extratropical regions of Western Australia. Part IIIB, (Epacridaceae-Lamiaceae). University of W.A. Press. Perth.