The families of flowering plants

L. Watson and M.J. Dallwitz

Pentastemonaceae Duyfjes

~ Stemonaceae.

Habit and leaf form. Juicy, unbranched herbs. ‘Normal’ plants. Plants green and photosynthesizing. Perennial; with a basal aggregation of leaves; rhizomatous (with scale leaves on the rootstocks). Stem growth not conspicuously sympodial (in fact, monopodial). Mesophytic. Leaves alternate; long petiolate; shortly sheathing; simple. Lamina entire; ovate; convergent pinnately veined; cross-venulate; cordate. Lamina margins entire.

Leaf anatomy. Stomata present; tetracytic. Hairs present; multicellular. Multicellular hairs multiseriate. The mesophyll containing crystals. The crystals raphides. Foliar vessels absent.

Axial (stem, wood) anatomy. Secondary thickening absent.

The vessel end-walls scalariform.

Root anatomy. Root xylem with vessels; vessel end-walls scalariform.

Reproductive type, pollination. Plants hermaphrodite, or polygamomonoecious (? — ‘flowers wholly or partly functionally unisexual, according to Duyfjes 1992).

Inflorescence, floral, fruit and seed morphology. Flowers aggregated in ‘inflorescences’; in cymes, or in racemes. Inflorescences axillary; emerging at ground level, pedunculate, compound, shorter than the leaves, the pedicels non-articulated. Flowers bracteate; bracteolate; small; regular; 5 merous; cyclic. Perigone tube present (urceolate).

Perianth of ‘tepals’; 5; joined; 1 whorled.

Androecium 5. Androecial members adnate (the connectives, the top of the perigone tube and the ovary forming a swollen disklike structure, bearing five (nectarial?) pouches each enclosing two thecae, one from each of the adjacent anthers); united with the gynoecium (the internal extensions from the staminal tube below the anthers fusing with the stigma lobes); coherent; 1 adelphous; 1 whorled. Stamens 5; isomerous with the perianth; with sessile anthers (more or less, the filaments joined laterally the beneath the anthers into a short fleshy tube, and this basal part extended to contact the stigma). Anthers basifixed; dehiscing via longitudinal slits; introrse; tetrasporangiate; unappendaged. Tapetum glandular. Pollen grains nonaperturate; 2-celled.

Gynoecium 3 carpelled. Carpels reduced in number relative to the perianth. The pistil 1 celled. Gynoecium syncarpous; synstylovarious; inferior. Ovary 1 locular. Gynoecium stylate. Styles 1; apical (short, thick). Placentation parietal (with three placentas). Ovules in the single cavity 20–50 (each placenta with ‘many’ ovules); horizontal, or ascending; arillate; anatropous; bitegmic; crassinucellate. Outer integument not contributing to the micropyle. Embryo-sac development probably Polygonum-type. Hypostase or similar structure present.

Fruit fleshy; indehiscent; a berry. Seeds copiously endospermic (with sarcotesta-like, hyaline exotestas and inflated arillodes). Endosperm not ruminate; oily. Embryo well differentiated (but minute). Cotyledons 1. Testa without phytomelan (?).

Geography, cytology. Paleotropical. Tropical. Sumatra.

Taxonomy. Subclass Monocotyledonae. Dahlgren et al. Superorder Liliiflorae; Dioscoreales. APG III core angiosperms; Superorder Lilianae; non-commelinid Monocot. APG IV Order Pandanales (as a synonym of Stemonaceae).

Species 2. Genera 1; only genus, Pentastemona.

General remarks. See Duyfjes (1992), van Heel (1992), Bouman and Devente (1992). Conspicuously different from Stemonaceae in habit, leaf form, floral morphology (perianth, androecium, gynoecium) and fruit type, and the available data also show different foliar stomatal patterns.

Illustrations. • Pentastemona egregia and P. sumatrana: Fl. Malesiana 11 (1993).

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: 5th March 2018.’.