Dioscorea piscatorum Prain & Burkill

Tubers more than one, clavate, arising in axils where the base of the stem touches the soil surface, unarmed or with short roots which may be indurated into thorns, some of which (teste KEITH) come above the soil; skin liver-coloured; flesh the red colour of diluted blood, intensely poisonous. Plant glabrous. Stems to 8 mm in diam. near the ground where there are 4-5 lines of confluent flat prickles; these give place upwards to scattered prickles and then more or less cease. Leaves except in their greater size and complete glabrousness as those of D. flabellifolia, attaining 18 by 14 cm, 9-nerved; petiole shorter by ¼ than the blade, with scattered small prickles on the back and the sides. Flowers unknown, acc. to KNUTH those of his 'D. borneensis' are formed on male inflorescences reaching a length of 70 cm.

The saponin in the tubers stupifies fish and the tubers are used as an alternative to Derris. Attention was drawn to this in 1908 by a Malay who exhibited the plant at an Agri-Horticultural Exhibition in Kuala Lumpur. BURKILL & HOLTTUM proved the effect (see BURK. Dict. 1935 822 ); GATER tried the tubers as an insecticide and found them effective, but less so than Derris. Being a substitute for Derris it shares the name tuba, and is known as tuba ubi (tuba yam) in the Malay Peninsula, tuba gunjo (wild tuba) among the Battaks of Tapanuli and tuba podeh gantung among the Dayaks of the Sanggau valley of Borneo. It is recorded that rasped tubers are put into the runnels of rice fields in Tapanuli 'to kill injurious worms'. Beyond all doubt the tubers are inedible to such animals as wild pig and are preserved from molestation by their poisonousness as well as by their thorny roots. Ignorance of the flowers is probably due to flowering not occurring until the climber has topped the forest.

Tubers are roasted and eaten. (They remain bitter if boiled.)