I Yam Not a Tortoise but a Plant
Dioscorea mexicana, commonly called Mexican Yam or Tortoise Plant, is native to Mexico, El Salvador, and Panama. Dioscorea is made up of around 600 species in the Dioscoreaceae family and has a world-wide distribution range. Originally in the Testudinaria genus and named after ‘Testudo,’ a genus of tortoise, it was later grouped into the genus Dioscorea.
The plant’s caudex (or modified stem) resembles the shell of a tortoise. The caudex itself is a partially exposed tuber that is covered in grayish-brown scales. It is divided into polygonal plates that are scored by deep furrows. This species typically goes dormant during the winter, though this year even without water for nearly four months the stem didn’t die back and still looks great, so we shall see what the future holds. From what I have experienced, heard from other growers, and also read, this plant sometimes either doesn’t die back during the winter or sends out a new stem earlier or later than expected, so watch the plant and not necessarily the calendar. The new stem can grow 15 to 20 feet in one season!
Dioscorea mexicana is dioecious meaning that the individual plants in the species are either male or female. The leaves are glossy green and heart-shaped. Flowers are greenish with dark purple centers and bloom in late summer. Although considered inconspicuous, I feel the male flowers add some visual interest. The caudex requires shade, usually provided by surrounding vegetation, while the vining portion of the plant needs full sun. It prefers to grow in a well-drained soil. Dioscorea mexicana is mostly propagated by seed, but although stubborn can be grown from cuttings.
If you can find one, this plant will have even the best plant enthusiasts talking and asking questions. Its easy winter care regimen (in most years) makes it a great choice for an exotic tropical look. During winter months greatly reduce the amount of water given to the plant; a light monthly watering is needed at most. I couldn’t find much information about and personally don’t know its hardiness but wouldn’t expose it to temps much below freezing for extended periods of time. Slowly bring it out of dormancy in the spring and give it lots of water during the hot growing summer season. Despite being nicknamed after a slow mover, Dioscorea mexicana quickly proves itself a crowd pleaser!
-Matt Fleming, Horticulturist