Hoya incrassata Warb. and Hoya crassicaulis Elmer x Kloppenb, both Philippine endemics have been always thought to be one species. Leaf architecture study of the two controversial species were examined to determine if they have similar characteristics in terms of leaf architecture, the main morphological character used in fossil studies and in taxonomic works dealing with sterile plant specimens. The unifying characters of the two species are the symmetrical and unlobed blade, acuminate apex, entire margin, pinnate primary vein, straight primary vein course, weak brochidodromous secondary vein, moderate relative secondary vein thickness, sinuous secondary vein course, loop-forming branches, enclosed by 3° or 4° arches, composite intersecondary veins, random reticulate tertiary vein, regular polygonal reticulate quaternary vein, looped ultimate marginal venation, and random areole arrangement. The characters blade length to width ratio, blade class and form, base shape, variation in secondary vein angle of divergence, and areole development delineates the two species apart. The study proved that H. incrassata and H. crassicaulis are two different species. Leaf architecture can be of great use when identifying and classifying seemingly similar plant species and sterile specimens. As both species are endemics to the Philippines, conservation ought to be massive as these species can be lost anytime with forest destruction. Conservation strategies could include forest protection and domestication. Keywords - Botany, leaf architecture, taxonomy, Hoya crassicaulis, Hoya incrassata, Philippines
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