A scanning electron microscope study of the stem structure in the West African Cane Palms (Calamoideae)

The canes of thirteen rattan taxa comprising two Calamus, three Eremospatha, five Laccosperma and three Oncocalamus were studied anatomically by scanning electron microscopy (SEM). Six out of the taxa tagged L. secundiflorum a, b, c; Oncocalamus sp. d, Oncocalmus sp. e and Calamus sp. f were unresolved herbarium voucher specimens many decades old. SEM photomicrographs revealed cell-tissue specific differences in anticlinal cell wall of the epidermis, fibrous sheaths, sheath parenchyma and phloem strands, leaf traces, and vessel diam- eter. Metaxylem vessel diameters varied between 20–212 µm in the outer peripheral zone and 90–310 µm in the central cylinder, except in L. secundiflorium c where the trend is reversed. Regression analysis of the metaxylem diameter values along radial distance shows large interspecific differences from central to outer cylinder. The weak R2 values (P ≤ 0.5) in nine of the thirteen species suggests that other unmeasured variables contribute to the observed trend. The structure of the unresolved voucher specimens appear to follow the same general trend in the identified specimens suggestive of phenotypic divergence between po- pulations brought about by developmental plasti- city. The leaf trace observed in Oncocalamus sp. e is unique and deserved to be examined more closely. A simple arithmetical expression indicat- ing structural synergy between protoxylem and metaxylem for possible volume ratio balance is included. (© 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)