Plectranthus escidentus N.E.Br. is a member of the family Lamiaceae, to which many aromatic plants such as the mints and sages belong. It differs from most members of the family in that it produces tuberous subterranean organs at the base of the stem, which can weigh as much as 1.8 kg per tuber. These organs are often used by local people as a food source. Storage organs in plants can be modified roots (carrot and sweet potato), stems (potato), or composed of leave bases (onion). In the case of P esculentus, there is a difference of opinion as to the exact ontogenetic origin of these organs, and whether they are roots, rhizomes, underground stems or root tubers. According to our observations, these tuberous, positively geotropic organs develop from axillary buds at the base of the stem, and even axillary buds along aerial parts of the stem. Their branching pattern follows the decussate phyllotaxis of the species, and flowering of some tubers has been observed. Anatomical studies show the presence of both primary and secondary vascular bundles arranged in a ring of vascular tissue. Therefore, these organs are true stem tubers. (C) 2003 Elsevier Science B.V. All rights reserved.
