Mitrasacme Labill.

Scientific Description

Common name. Mitreworts. Family Loganiaceae.

Separated from Mitrasacme sens lat along with Schizacme and Phyllangium by C.R.Dunlop (1996).

Habit and leaf form. Herbs (erect, prostrate or pendent). Annual, or perennial. Leaves cauline. Young stems cylindrical. Occasionally rhizomatous (or stoloniferous (when perennial)). Self supporting (although sometimes prostrate or pendent). Helophytic, or mesophytic, or hydrophytic (M. secedens). Heterophyllous. Leaves variable in size minute, or small, or medium-sized; not fasciculate; opposite, or whorled (but usually only appearing so); decussate; 2 per whorl (when appearing so); not decurrent on the stems; ‘herbaceous’; sessile, or subsessile, or petiolate (rarely). Petioles when present wingless. Leaves simple; epulvinate. Leaf blades dorsiventral; entire; flat; linear, or ovate, or obovate, or oblong, or elliptic (rarely narrow, pungent or attenuate); 1 -nerved; pinnately veined; cross-venulate. Mature leaf blades adaxially glabrous, or pilose; abaxially glabrous, or pilose. Leaves with stipules (reduced to a connate sheath). Stipules interpetiolar (or represented by a stipular sheath); ochreate; much reduced. Leaf blade margins entire; flat. Leaf anatomy. Hairs present, or absent. Unicellular hairs present, or absent.

Reproductive type, pollination. Fertile flowers hermaphrodite. Unisexual flowers absent. Plants hermaphrodite. Plants homostylous.

Inflorescence and flower features. Flowers aggregated in ‘inflorescences’ (usually), or solitary; terminal to axillary. Inflorescence few-flowered to many-flowered. Flowers in umbels (when not solitary). Inflorescences simple to compound. The terminal inflorescence unit racemose. Inflorescences terminal to axillary; ascending, or pendent. Flowers pedicellate; ebracteolate; small; regular; 4 merous; cyclic; tetracyclic. Free hypanthium absent. Perianth with distinct calyx and corolla; 8; 2 -whorled; isomerous. Calyx present; 4; 1 -whorled; gamosepalous; lobed; lobulate. Calyx lobes markedly shorter than the tube. Calyx segments entire. Calyx spreading; hairy, or glabrous; exceeded by the corolla, or more or less equalling the corolla; campanulate; regular; persistent. Calyx lobes ovate. Corolla present; 4; 1 -whorled; gamopetalous; lobed; lobulate. Corolla lobes markedly shorter than the tube. Corolla valvate; regular; glabrous abaxially; usually glabrous adaxially (rarely, in the throat); plain, or with contrasting markings; usually white, or white to orange, or white to brown. Corolla lobes ovate. Androecium present. Androecial members definite in number. Androecium 4. Androecial members free of the perianth, or adnate (partly); all equal; free of one another; 1 -whorled. Androecium occasionally including staminodes. Stamens 4; usually remaining included, or becoming exserted; all more or less similar in shape; isomerous with the perianth; all alternating with the corolla members; filantherous (or almost sessile). Filaments glabrous, or hairy (at base); filiform. Anthers basifixed; extrorse, or latrorse, or introrse; unappendaged, or appendaged (M. graminea). The anther appendages apical (linear and subplumose). Anthers apiculate. Gynoecium 2 carpelled. The pistil 2 celled. Carpels reduced in number relative to the perianth. Gynoecium syncarpous; synstylovarious to eu-syncarpous; superior. Ovary plurilocular; 2 locular. Gynoecium stylate. Styles 2; partially joined; apical; persistent. Stigmas 2; capitate. Ovules 30–50 per locule.

Fruit and seed features. Fruit 0–7 mm long; persistent; non-fleshy; not hairy, or hairy (scabrous to papillose-squamulose in upper part); dehiscent (except M. serpyllifolia with seeds too large to be shed by capsule dehiscence); a capsule. Capsules loculicidal, or septicidal (in M. gentianea). Dispersal unit the seed. Seeds small. Cotyledons 2.

Geography, cytology, number of species. Australian and Paleotropical. Native of Australia. Endemic to Australia. Australian states and territories: Western Australia, South Australia, Northern Territory, Queensland, New South Wales, Victoria, Australian Capital Territory, and Tasmania. Northern Botanical Province and Eremaean Botanical Province. Absent from south-western WA. A genus of 54 species; 19 species in Western Australia; 9 endemic to Western Australia.

Additional comments. Name from the Greek mitre (headdress or head band), and akme (highest point), in reference to the capsule having the appearance of the ecclesiastical mitre.

Etymology. From the Greek for "cap, mitre" and "high point, flower"; refers to the fancied resemblance of the flower of M. pilosa to a bishop's mitre.