Anatomical characteristics of Nigerian variants of Caladium bicolor (Aiton) Vent. (Araceae)

Four Caladium bicolor variants collected from different parts of Nigeria were subjected to anatomical comparison to enhance the taxonomic status of the species. Fresh samples (leaf and petiole) of these variants were fixed in formalin, acetic acid and alcohol (FAA), dehydrated in alcohol series, peeled or sectioned. Peeled specimens were stained with safranin, while sectioned ones were stained with Alcian blue and counterstained with safranin. Good preparations were mounted on slides, viewed and photographed with Optika B-1000 FL LED microscope. Epidermal cells from the variants are mainly pentagonal-hexagonal but rarely heptagonal while the anticlinal cell walls are mainly straight and partly arced/curved. Variants A, B and D are amphistomatic while variant C is hypostomatic. Isotricytic, anisocytic, tetracytic, anomocytic and contiguous stomata were observed among the taxa. The stomata index (SI) varied from 4.35 to 11.76 on the adaxial surface, and from 6.25 to 47.62 on the abaxial surface. Calcium oxalate crystals (druses, 8.18 to 19.09 µm and raphides, 21.82 to 68.18 µm) occur in all variants. Raphides are predominantly found in the petiole while druses and raphides are found in the midrib and petiole. The shapes of the adaxial surface of the midrib are relatively different from each other, and include curved (convex) and flat surfaces. The leaf lamina comprised one layer of palisade and spongy mesophylls each. The number of vascular bundles varied from 11 to 23 in the midrib. These characters can be used to distinguish these taxa especially when combined with the existing data on the species. The similarities among these variants point towards the same evolutionary origin; however may suggest that intraspecific or interspecific hybridizations may have produced the variants. Key words: Amphistomatic, Caladium, druses, hypostomatic, midrib, petiole, raphides.