Dioscorea x discolour: Yam Plant
If you have a large room with plenty of sun you might like the idea of covering the windows in summer with the green foliage of an undemanding plant that sheds its leaves and dies back in the autumn, thus letting more light in again. Ideal for this purpose is dioscorea, a tuberous plant with a growing season from spring until autumn, during which time it attains a good size.
The hybrid is derived from several species that are not definitely known, but in all probability included among their number are D. multicolor chrysophylla, D. amarantoides and D. vittata from Brazil. All three are relatively small climbers, growing to a length of 2 m (6 ft) in indoor cultivation. The leaves are about 10 to 15 cm (4 to 6 in) long, variegated, often with golden glints and patches and a pale area round the midrib, but almost always reddish violet on the underside.
Of the larger climbers, D. sansibarensis is recom-mended. This is often grown inin botanical gardens under the wrong name of D. macro lira. The leaves are truly large, in robust specimens up to 30 cm (1 ft) across, broadly heart-shaped with auricles and tapering to a long point which serves as run-off for excess water from the leaves. The conspicuous venation is particularly attractive and the aerial tubers formed in the leaf axils by means of which the plant spreads and multiplies are of botanical interest. This characteristic is common to a number of species and has given its name to one — D. bulbifera, a well-known edible plant of the tropics (both the small aerial tubers and the large underground are edible).
The best known edible yam is D. batatas, native to south-east Asia. Not only is it a good house plant but it will also grow outdoors in the garden, without protection, climbing over shrubs and the trunks of trees in summer.
Yams should be grown in rich, rather heavy, such as John Innes potting compost No. 3. They are undemanding, rapidly growing plants; even the green-leaved species have no special light requirements, needing only a rich diet. Propagation is by means of the small aerial tubers and by cuttings. The tubers should be lifted for the winter and stored in a warm, dry place until time for potting up or planting out again in spring.