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(Last Modified On 10/26/2012)
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(Last Modified On 10/26/2012)
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Genus
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DIOSCOREA L.
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PlaceOfPublication
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Sp. P1. 1032. 1753
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Reference
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C. V. Morton, Carn. Inst. Wash. Publ. 461:241-253. 1936.
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Description
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wining vines; leaves simple, alternate or opposite, petiolate, usually cordate at base, acuminate, entire or lobate, glabrous or pubescent with simple hairs, not tendril-bearing, palmately veined, the secondary veins reticulate; flowers regular, unisexual (dioecious); perianth segments 6, similar, equal, ovate to linear-oblong, connate at base; stamens 6, or 3 (rarely alternating with 3 staminodia), borne on perianth segments or on a central disk, free or connate; anthers small, free, open- ing by longitudinal slits, introrse or extrorse; rudimentary ovary present or absent in the staminate flowers; pistillate flowers with or without minute staminodia; ovary inferior, linear or oblong, 3-celled; ovules 2 in each cell, superposed, pendulous, anatropous; styles 3, short; fruit a loculicidally dehiscent, 3-valved capsule; seed winged at base or all around.
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Note
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The cultivated yams, often called finame in tropical America, belong to this genus. The following cultivated species, and perhaps others, may be naturalized to some extent in Panama: Dioscorea alata L., D. bulbifera L., and D. cayennensis Lam. Since the cultivated plants are usually sterile, these species have been placed in the alternative key based on sterile specimens. No descriptions of them are provided. A specimen of an additional native species, probably undescribed, has been collected near Cana, but the material at hand is in fruit only.
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Key
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a. Fertile stamens 6. b. Leaf blades 3- to 5-lobed; stems and petioles winged; rhachis and perianth segments pubescent; stems twining to the left - 7. D. TRIFIDA bb. Leaf blades entire. c. Rhachis, perianth segments, and pedicels pubescent; leaves alter- nate, not pellucid-lineolate. d. Leaf blades glabrous beneath, ovate-lanceolate; stems twining to the right; filaments central, partly connate; anthers opening outwardly - -- --1. D. SAPINDOIDES dd. Leaf blades densely soft-pilose beneath, suborbicular; stems twining to the left; filaments borne on the perianth segments, free from each other; anthers opening inwardly - 8. D. CYMOSULA cc. Rhachis, perianth segments and pedicels glabrous; leaves and stems glabrous. d. Leaves partly opposite or subopposite, conspicuously pellucid- lineolate by transmitted light; stems bearing spines at base of the larger leaves; stems twining to the left; flowers solitary, sessile; anthers opening inwardly--- 2. D. UROPHYLLA dd. Leaves alternate, not pellucid-lineolate; stems unarmed, twining to the right; flowers not solitary, or if so, not sessile; anthers opening outwardly e. Filaments slender (0.5 mm. long); leaf blades small (not over 4 cm. long), merely rounded at base, 5-nerved -5. D. PANAMENSIS ee. Filaments obsolete; leaf blades larger, cordate at base, 9- nerved --- 9. D. MACROSTACHYA aa. Fertile stamens 3; plants wholly glabrous; leaves alternate; stems un- armed. b. Anther cells separated by a broad connective; staminodia 3, bifid; flowers sessile, fasciculate ----- 10. D. POLYGONOIDES bb. Anther cells contiguous; staminodia none; flowers pedicellate, soli- tary or rarely in clusters. c. Seeds winged at base only. d. Filaments very short, inserted on a fleshy, central disk; perianth purple; flowers solitary or clustered -- 6. D. RACEMOSA dd. Filaments obvious, conspicuously enlarged and connate at base; perianth green; flowers always solitary. e. Capsules acute - ---- 4. D. LEPIDA ee. Capsules rounded at apex---. 3. D. CONVOLVULACEA cc. Seeds winged all around; staminate flowers borne in stalked clusters along rhachis -_ - 11. D. STANDLEYI ALTERNATIVE KEY BASED ON STERILE OR FRUITING PLANTS a. Stems and petioles winged. b. Leaf blades deeply 3- to 5-lobed; rhachis and perianth segments pubescent; stems twining to the left - 7. D. TRIFIDA bb. Leaf blades not lobed; rhachis and perianth segments glabrous; stems twining to the right - D. ALATA aa. Stems and petioles not winged; leaf blades entire. b. Leaves opposite, at least in part; stems spiny at base of the larger leaves; leaves pellucid-lineolate. c. Stems twining to the left; capsule valves woody -2. D. UROPHYLLA cc. Stems twining to the right - D. CAYENNENSIS bb. Leaves alternate; stems unarmed; leaves not pellucid-lineolate. c. Rhachises and ovaries densely pubescent; stems and petioles more or less pubescent. d. Stems twining to the right; leaf blades glabrous beneath, ovate- lanceolate - _ - - --1. D. SAPINDOIDES dd. Stems twining to the left; leaf blades densely soft-pilose be- neath, suborbicular -8. D. CYMOSULA cc. Rhachises and ovaries glabrous or merely scabrous; leaves and stems glabrous. d. Leaf blades small (not over 4 cm. long), lanceolate or ovate- lanceolate, rounded at base, 5-nerved; stems twining to the right - 5. D. PANAMENSIS dd. Leaf blades larger, broadly ovate or suborbicular, cordate at base, 9- to 11-nerved. e. Seeds winged at base only. f. Stems twining to the left-- D. BULBIFERA ff. Stems twining to the right. g. Capsules acute -4. D. LEPIDA gg. Capsules rounded at apex -3. D. CONVOLVULACEA ggg. Capsules unknown - 6. D. RACEMOSA ee. Seeds winged all around. f. Stems twining to the left; leaf blades abruptly short- acuminate; capsules about 1.7 cm. long - - 10. D. POLYGONOIDES ff. Stems twining to the right. g. Capsules 2.5-3 cm. long; stigmas subsessile -9. D. MACROSTACHYA gg. Capsules about 1.5 cm. long; stigmas borne on style 1 mm. long -11. D. STANDLEYI
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