Comparative morphoanatomical studies of south eastern Nigerian representatives of Oldenlandia L. (Rubiaceae)

Abstract

Leaf and stem anatomical structure of the four Oldenlandia L. (O. affinis (Roem. & Schult.) DC., O. corymbosa L., O. herbacea (Linn.) Roxb., and O. lancifolia (Schumach) DC.) from some parts viz. Ogbokor (Edo State), Obiga-Asa (Abia State), IITA staion Onne (Rivers State), and Agricultural farm Uniport (Rivers State) Nigeria were examined by light microscopy. The epidermal cells are pentagonal to polygonal with straight, curved or wavy anticlinal walls, and paracytic stomata. All the species have dorsiventral leaf with the leaf vein vascular bundles embedded in the spongy mesophyll. The midribs vascular bundles form an arc enclosed by parenchymatous endodermal cells. O. herabcea is amphistomatic while the other species are hypostomatic. Raphide bundles were seen only in the lamina of O. corymbosa. Tuft hair is absent in O. herbacea but occurred on the adaxial leaf surfaces of O. affinis, O. corymbosa, and O. diffusa. The stem of O. diffusa is terete while other species have quadrangular stem. Papillae occurred on the adaxial epidermis of O. affinis and O. corymbosa. The stem pith thickness (PT)/cortical thickness (ET) ratio varied among the species. Notable diagnostic features in these species include the PT/ET ratio, layers of cortex in the stem, occurrence of tuft hairs on the leaf veins and surface, presence or absence of raphides and papillose, layer of abaxial and adaxial cortex in the midrib, and amphistomatatic or hypostomatic leaf.