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The families of flowering plants.                                                                                                                                                                

Pentastemonaceae Duyfjes.

                        

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~Stemonaceae

Habit and leaf form. Juicy, unbranched herbs. ‘Normal’ plants. 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 calcium oxalate crystals. The mesophyll crystals raphides. Vessels absent.

Stem anatomy. Secondary thickening absent. 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).

Perianthof ‘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 3 core angiosperms; Superorder Lilianae; non-commelinid Monocot; 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).

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