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The families of flowering plants

L. Watson and M.J. Dallwitz

Mitreolaceae Watson, informal

~ Loganiaceae.

Habit and leaf form. Sub- shrubs (in Schizacme), or herbs (mostly). Plants non-succulent. Annual, or perennial; with a basal aggregation of leaves, or without conspicuous aggregations of leaves. Leaves opposite (mostly), or whorled; in M. minima sometimes 3 per whorl (at the lower nodes); ‘herbaceous’, or leathery (?), or fleshy; imbricate, or not imbricate; petiolate to sessile, or perfoliate; connate (via the stipular sheaths); simple. Lamina entire; one-veined, or pinnately veined, or palmately veined. Leaves stipulate to exstipulate. Stipules interpetiolar (the opposite petioles connected across the node by recognisable but small and joined stipules or a stipular membrane); with colleters, or without colleters (?).

Leaf anatomy. Hairs present, or absent; when present, eglandular. Complex hairs absent.

Axial (stem, wood) anatomy. Young stems cylindrical, or oval in section. Internal phloem present. Secondary thickening anomalous. The anomalous secondary thickening from a single cambial ring.

The vessel end-walls scalariform, or simple. ‘Included’ phloem present.

Reproductive type, pollination. Plants hermaphrodite, or gynomonoecious; homostylous.

Inflorescence, floral, fruit and seed morphology. Flowers solitary, or aggregated in ‘inflorescences’; when solitary, terminal, or axillary; when aggregated, in cymes, or in racemes, or in umbels. The ultimate inflorescence units cymose. Inflorescences scapiflorous, or not scapiflorous; terminal and axillary, or axillary; with involucral bracts (each flower in Phyllangium enclosed by a bilobed, foliaceous involucre), or without involucral bracts. The involucres of Phyllangium accrescent. Flowers bracteate, or ebracteate; ebracteolate (assuming the involucre of Phyllangium is not bracteolar); small; regular; 5 merous (in Mitreola), or 4 merous (in Mitrasacme and segregates); tetracyclic. Floral receptacle with neither androphore nor gynophore. Free hypanthium absent. Hypogynous disk absent.

Perianth with distinct calyx and corolla, or petaline (Phyllangium); 4, or 8, or 10; 2 whorled; isomerous. Calyx 4, or 5; 1 whorled, or 2 whorled (two decussate pairs in Schizacme archeri); gamosepalous (usually), or polysepalous (Schizacme archeri); regular (usually), or unequal but not bilabiate (Schizacme, with one pair of sepals or lobes larger); persistent. Corolla 4 (Mitrasacme and segregates), or 5 (Mitreola); 1 whorled; gamopetalous (hairy inside, or bearded in the throat). Corolla lobes markedly shorter than the tube, or about the same length as the tube. Corolla nearly always valvate, or imbricate (in some Mitreola species and Schizacme archeri); urceolate (Mitreola), or campanulate, or hypocrateriform; regular; white, or yellow, or pink, or purple (or mauve); not fleshy.

Androecium 4 (Mitrasacme), or 5. Androecial members adnate (to the corolla tube); all equal; free of one another; 1 whorled. Androecium exclusively of fertile stamens, or including staminodes. Staminodes when present, 1–3; external to the fertile stamens. Stamens 4, or 5; inserted near the base of the corolla tube to midway down the corolla tube; isomerous with the perianth; oppositisepalous; alternating with the corolla members; filantherous (the filaments long to very short). Anthers dorsifixed to basifixed; dehiscing via longitudinal slits; extrorse to introrse (e.g., all states exhibited in Mitrasacme); appendaged (sometimes, in Mitrasacme and Mitreola), or unappendaged. The anther appendages apical (via a straight or curved prolongation of the connective). Pollen grains aperturate; 3 aperturate; colporate.

Gynoecium 2 carpelled. Carpels reduced in number relative to the perianth. The pistil 2 celled. Gynoecium syncarpous; semicarpous to synovarious (in Schizacme and some Mitrasacme and Phyllangium species), or eu-syncarpous to synstylous (i.e., the two styles then separate basally and usually but not always joined above, cf. Apocynaceae); superior (usually), or partly inferior (Mitreola, Phyllangium). Ovary 2 locular. Gynoecium median. Ovary sessile. Gynoecium stylate. Styles 1 (mostly, though basally split), or 2 (sometimes, in Mitrasacme sensu lato); apical, or lateral. Stigmas 1, or 1–2; of Mitreola minima wet type; papillate. Placentation axile, or axile to apical (the placentas peltate). Ovules differentiated; 5–50 per locule (‘several to many’); hemianatropous (Mitrasacme), or anatropous (?); unitegmic; tenuinucellate. Endothelium not differentiated. Hypostase absent. Endosperm formation cellular to nuclear (intermediate, in Mitrasacme). Embryogeny solanad (in Mitrasacme).

Fruit non-fleshy. The fruiting carpel when semicarpous, dehiscent; a follicle. Fruit when syncarpous, i.e. usually, dehiscent (truncate or bilobed above), or a schizocarp (sometimes at least partially, in Mitrasacme and Schizacme). Mericarps when splitting into carpels, 2; when recognisable, comprising follicles (splitting along the interior margins of the carpels). Fruit when not assignable to schizocarpic, a capsule (compressed at right angles to the septum, apically truncate or bilobed — i.e., the carpels then constituting partial mericarps). Capsules denticidal, or septicidal and loculicidal (dehiscing apically along the interior margin (loculicidally between the horns) of the carpels, which may be free or more or less connate). Fruit 20–100 seeded (‘many’). Seeds endospermic; small; not conspicuously hairy; wingless (globose or compressed). Embryo well differentiated. Cotyledons 2. Embryo straight.

Physiology, phytochemistry. Alkaloids absent (at least, from screened species of Mitrasacme). Verbascosides not detected. Cornoside not detected. Iridoids detected; ‘Route I’ type.

Special distinguishing feature. Lamina tip not abaxially pouched (i.e., not as in Saccifoliaceae).

Geography, cytology. Temperate, sub-tropical, and tropical. North and tropical America, tropical and subtropical Asia and Australia (Mitreola); Indomalesia, eastern Asia, Australia and New Zealand (Mitrasacme sensu lato). 2n = 20 (Mitreola. Supposed basic chromosome number of family: 10. Ploidy levels recorded: 2.

Taxonomy. Subclass Dicotyledonae; Tenuinucelli. Dahlgren’s Superorder Gentianiflorae; Gentianales. Cronquist’s Subclass Asteridae; Gentianales. APG 3 core angiosperms; core eudicot; Superorder Asteranae; lamiid; Order Gentianales (as a synonym of Loganiaceae?).

Species about 70. Genera 4; Mitreola, Mitrasacme, Phyllangium, Schizacme.

General remarks. See Leeuwenberg 1980, under Loganiaceae. Mitreola and Mitrasacme (plus the recent segregates from the latter, Schizacme and Phyllangium) are long standing and closely related members of the traditional, manifestly heterogeneous Loganiaceae (cf. their proximity in the Genera Plantarum (1876)). Struwe and Albert (1994) retained them with Logania in their sensu stricto version of Loganiaceae. On the basis of the more detailed descriptions compiled here, however, they are no closer to Logania than to Gentianaceae. The range of gynoecia and fruits is reminiscent of Apocynaceae, which seem distant in other respects. See comments under Loganiaceae.

Illustrations. • Phyllangium distylis, P. paradoxum and Schizacme montana (all as Mitrascacme spp.): Hooker, Fl. Tasmaniae (1860). • Mitreola paniculata: Hook. Ic. Pl. 9 (1852). • Mitreola paniculata: Fl. Brasil. 6 (1860–68). • Mitreola petiolata: Fl. Brasil. 6 (1860–68).

We advise against extracting comparative information from the descriptions. This is much more easily achieved using the DELTA data files or the interactive key, which allows access to the character list, illustrations, full and partial descriptions, diagnostic descriptions, differences and similarities between taxa, lists of taxa exhibiting or lacking specified attributes, distributions of character states within any set of taxa, geographical distribution, genera included in each family, and classifications (Dahlgren; Dahlgren, Clifford, and Yeo; Cronquist; APG). See also Guidelines for using data taken from Web publications.

Cite this publication as: ‘Watson, L., and Dallwitz, M.J. 1992 onwards. The families of flowering plants: descriptions, illustrations, identification, and information retrieval. Version: 13th March 2017.’.