On the occurrence of root thorns on a Central American palm

Abstract

The palm Cryosophila guagara Allen bears three types of adventitious roots on the stems of young plants, prop roots, trunk roots, and crown roots. The latter two are modified into thorns; but crown roots are lacking in older plants. Crown roots arise endogenously near the apex of the stem and grow vertically downward in the stem tissues, emerging near the attachment of an enveloping leaf sheath. The root then changes its direction of growth at the site of leaf attachment, grows vertically upward to the top of the sheath, and ultimately gives rise to a pendulous, branched thorn. Trunk roots or spines arise as laterals from the bases of crown roots embedded in the tissues of the stem. The conversion of a root apex to a thorn involved the cessation of meristematic activity, the acropetal extension of tissue differentiation with an associated attenuation of the conical root apex, and the extensive development of cortical and stelar sclerenchyma. The root cap does not contribute to the thorn.