Genus 1, species 2. Tropics. Used as ornamental plants and for plaiting-work; the tubers yield starch (arrowroot) and are edible when cooked. Tacca Forst.
[FAMILY 37.] DIOSCOREACEAE
Root-stock tuberous. Stem twining. Leaves alternate, net-veined, usually cordate. Flowers in racemes, inconspicuous, regular, unisexual. Stamens 6. Ovary inferior, 3-celled. Ovules 2 in each cell, superposed, inverted. Styles or style-branches 3. Embryo enclosed in a horny or cartilaginous albumen.—Genera 2, species 45. (Plate 21.)
Fruit a berry. Seeds not winged.—Species 3. North Africa. The tubers are eaten and used in medicine; the berries are poisonous. (Tamnus
Juss.) Tamus L.
Fruit a capsule. Seeds winged.—Species 40. Tropical and South Africa.
Some are cultivated for their edible tubers (yams) or used in medicine; others are poisonous. (Including Testudinaria Salisb.) (Plate 21.) Dioscorea L.
SUBORDER IRIDINEAE
[FAMILY 38.] IRIDACEAE
Herbs or undershrubs. Inflorescence terminal. Flowers hermaphrodite. Perianth with 6 petaloid segments. Stamens 3, inserted opposite the outer perianth-segments. Anthers turned outwards. Ovary inferior, 3-celled, rarely (Hermodactylus) 1-celled. Style-branches usually divided or dilated. Ovules numerous, inverted. Fruit a loculicidal capsule. Embryo enclosed by the horny albumen.—Genera 39, species 600. (Plate 22.)
1. Flowers solitary, terminal, sometimes surrounded by several axillary flowers, each flower with a spathe. Perianth regular; inner and outer segments nearly equal. Leaves not exactly 2-ranked. Stem short or almost wanting. [Subfamily CROCOIDEAE.] 2
Flowers in various inflorescences, rarely spathes solitary, but 2- or more-flowered or (if 1-flowered) the outer perianth-segments very different from the inner ones. Leaves 2-ranked, folded one above the other, rarely
(Geosiris) reduced to scales. Stem distinctly developed. 5
2. Stem underground, very short. Perianth-tube very long. 3
Stem partly above ground. Perianth-tube short or moderately long. 4
3. Style-branches undivided, stigmatose inside. Perianth red or violet, rarely white with red streaks.—Species 6. South Africa (Cape Colony). Syringodea Hook. fil.
Style-branches many-lobed or many-parted, stigmatose at the top.—Species
3; one of them only cultivated. North-West Africa. Used as ornamental plants; the tubers are edible. The cultivated species
(C. sativus L.) yields the saffron, which is used as a condiment and for dyeing. Crocus L.
4. Leaves crowded at the top of the very short stem. Perianth with a rather long tube, yellow or violet. Filaments united into a tube. Style-branches dilated above, petal-like.—Species 3. South Africa (Cape
Colony). Used as ornamental plants. Galaxia Thunb.
DIOSCOREACEAE.