Nodal spine pairs present in the mimosoid Prosopis juliflora are not stipules but define a distinct class of lateral organs

Abstract

The descriptions of Prosopis juliflora of subfamily mimosoideae in the family leguminosae, given in the floras of arid and semi-arid regions of the world, including the flora of Delhi, state that the spine pairs seen in association with compound leaf on nodes are stipules. The suggestions that spines are stipules were tested by morphological and histological examination of nodes of P. juliflora plants growing in the Arawalli range at New Delhi. The nascent nodes on growing branches of P. juliflora were observed to produce a pair of knife-like free bifacial stipules together with a leaf and a pair of spines. The stipules were missing from the mature nodes of the same branches whose young nodes carried stipule pairs, suggesting that the stipules were deciduous whereas leaves and spines were persistent. Anatomically, spines were observed to be appendages to stem and located adjacent to leaf petiole away from stipules. Vasculature of stipules was independent. The observations allowed the conclusion that P. juliflora nodes form regular stipules and spines produced on them are stem-like distinct lateral organs. It is suggested that nodal spine pairs borne on plant nodes in general are lateral organs different from stipules, leaves and secondary inflorescences.