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The families of flowering plants.                                                                                                                                                                

Periplocaceae Schltr.

                        

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~Asclepiadaceae, Apocynaceae

Habit and leaf form. Shrubs (or shrublets), or lianas (commonly), or trees (rarely), or herbs (rarely); laticiferous. The herbs perennial; sometimes tuberous. Self supporting, or climbing; the climbers stem twiners. Mesophytic, or xerophytic. Leaves opposite; petiolate; simple; epulvinate. Lamina entire; linear to obovate; pinnately veined; cross-venulate. Leaves exstipulate (and no stipular colleters). Lamina margins entire.

General anatomy. Plants with laticifers (non-articulated, branched or not).

Leaf anatomy. Stomata paracytic, or anomocytic, or anisocytic.

Lamina with secretory cavities (laticifers accompanying the veins). Secretory cavities containing latex. Minor leaf veins without phloem transfer cells (Periploca).

Stem anatomy. Secretory cavities present. Nodes unilacunar (the petiolar trace single, gutter-shaped). Primary vascular tissue bicollateral. Internal phloem present. Secondary thickening developing from a conventional cambial ring, or anomalous; via concentric cambia, or from a single cambial ring (?). ‘Included’ phloem present, or absent (?). Wood storied (Periploca); parenchyma apotracheal (predominantly, in Periploca), or paratracheal (?).

Reproductive type, pollination. Plants hermaphrodite (usually), or dioecious. Pollination entomophilous; mechanismconspicuously specialized (with pollen transference involving ‘translators’ — spoon- or funnel-shaped structures arising from the stylehead between the anthers, which conceal the stigmatic surfaces from pollinators and into each of which the granular pollen from adjacent half-anthers is shed. A sticky disk on the base of the translator adheres to the head of a visiting insect, which carries off the translator and its pollen contents).

Inflorescence, floral, fruit and seed morphology. Flowers aggregated in ‘inflorescences’; in cymes. The ultimate inflorescence unit cymose. Inflorescences cymose, neither umbelliform nor racemose. Flowers bracteate; small (usually), or large (and showy, rarely); regular; 5 merous; cyclic; tetracyclic. Free hypanthium present. Hypogynous disk absent.

Perianth with distinct calyx and corolla; 10; 2 whorled; isomerous. Calyx 5; 1 whorled; gamosepalous (the tube short). Calyx lobes markedly longer than the tube. Calyx regular; imbricate, or valvate. Corolla 5; 1 whorled; appendiculate (usually, from the corolla tube, or at the sinuses between the lobes), or not appendiculate; gamopetalous; contorted (usually), or valvate; regular.

Androecium 5. Androecial members free of the perianth (on the hypanthium), or adnate; free of the gynoecium; coherent (via the anthers, the filaments free); 1 adelphous; 1 whorled. Androecium exclusively of fertile stamens. Stamens 5; inserted when epipetalous, near the base of the corolla tube; isomerous with the perianth; oppositisepalous. Filaments not appendiculate. Anthers cohering (by their tips into a sheath, and adherent to the stylehead); basifixed; non-versatile; dehiscing via longitudinal slits; introrse; four locular; tetrasporangiate; appendaged (usually, but via connective extensions only, not wings), or unappendaged. The anther appendages apical, or dorsal, or lateral. Endothecium developing fibrous thickenings. Microsporogenesis simultaneous. The initial microspore tetrads tetrahedral, or isobilateral, or T-shaped, or linear. Anther wall initially with one middle layer, or initially with more than one middle layer; of the ‘dicot’ type. Tapetum glandular. Pollen shed in aggregates; in tetrads (these variously tetrahedral, rhombiodal, linear, etc., and the tetrads readily separating, at most only weakly coherent into loose massules rather than pollinia). Pollen grains aperturate; 3–6 aperturate; porate; 2-celled, or 3-celled.

Gynoecium 2 carpelled. Carpels reduced in number relative to the perianth. The pistil 2 celled. Gynoecium syncarpous; synstylous (the separate carpels united only by the common stylehead); superior. Carpel 5–50 ovuled. Placentation marginal (ventral). Ovary alternatively interpretable as 2 locular (the separate ovaries being viewed as the ‘locules’ of a ‘syncarpous’ gynoecium). Gynoecium median; stylate. Styles 2; partially joined (free below, but joined at the distended stylehead, cf. Asclepiadaceae). Placentation equivalent to axile (ventral in the discrete ‘locules’, corresponding with axillary in Apocynaceae). Ovules 5–50 per locule (to ‘many’); pendulous; anatropous; unitegmic; pseudocrassinucellate. Embryo-sac development Polygonum-type. Polar nuclei fusing prior to fertilization. Antipodal cells formed; 3; not proliferating; ephemeral. Synergids hooked. Endosperm formation nuclear. Embryogeny solanad.

Fruit non-fleshy; an aggregate (the units usually paired), or not an aggregate (by abortion of one of them); dehiscent; of two ‘follicles’ or one undeveloped, the placenta thick and cylindric bearing the seeds on denticles. Seeds endospermic. Endosperm oily. Seeds conspicuously hairy (with a terminal coma of long, silky hairs); wingless. Embryo well differentiated. Cotyledons 2. Embryo straight.

Physiology, biochemistry. Not cyanogenic. Alkaloids present. Iridoids not detected (?). Proanthocyanidins present; cyanidin. Ellagic acid absent (Periploca). Arbutin absent. Saponins/sapogenins absent. Aluminium accumulation not found. C3. C3 physiology recorded directly in Cryptostegia.

Geography, cytology. Holarctic, Paleotropical, and Cape. Temperate to tropical. Old World, especially tropical Africa. 2n = 22, 24. 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 Apocynaceae).

Species 200. Genera 45–50; Asterostemma, Atherandra, Atherolepis, Aechmolepis,Baeolepis, Baroniella, Baseonema, Batesanthus, Camptocarpus,Chlorocyathus, Cryptolepis, Cryptostegia, Curroria,Cyprinia, Decalepis, Ectadiopsis, Ectadium, Epistemma,Finlaysonia, Gonglyosperma, Gonocrypta, Gymnanthera,Gymnolaema, Harpanema, Hemidesmus, Ischnolepsis, Kompitsia,Macropelma, Mangenotia, Meladerma, Menabea, Mitolepis,Mondia, Myriopteron, Oxystelma, Parquetina, Pentagonanthus,Pentanura, Pentopetia, Pentopetiopsis, Periploca, Phyllanthera,Raphionacme, Sacleuxia, Sarcorrhiza, Schlechterella,Socotranthus, Stelmacrypton, Streptocaulon, Tacazzea,Tanulepis, Telectadium, Triodoglossum, Utleria, Zacateza,Zygostelma.

General remarks. See Swarupanandan, Mangaly, Sonny, Kishorekumar and Chand Basha (1996).

Economic uses, etc. Some cultivated ornamentals (Periploca), and Cryptostegia has been used as a source of natural rubber.

 Illustrations:

  • Technical details: Taccazea (Thonner).
  • Androecial details: Periploca.
  • Periploca graeca: Bot. Reg. 803, 1824.
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