Stomatal novelties in Vincetoxicum arnottianum (Asclepiadeae: Asclepiadoideae: Apocynaceae)

Stomatal multiplicity in the foliar epidermis is an intriguing feature found rarely in dicotyledonous plants. Here we present Vincetoxicum arnottianum as an addition to the list of taxa possessing multiple stomata. We sampled V. arnottianum from sixteen different populations representing the whole distribution range of this species in Pakistan. Detailed investigation of both adaxial and abaxial epidermal surfaces under light microscope revealed ten major stomatal types and thirty six subtypes viz. paracytic (five subtypes), anisocytic (three subtypes), tetracytic (two subtypes), laterocytic (thirteen subtypes), stephanocytic (four subtypes), brachyparahexacytic (one subtype), anomocytic and actinocytic. Among these types, we report polar paracytic (with six subtypes) and pseudoholoparacytic (with two subtypes) as novel stomatal types based on their unique architecture. Scanning electron microscopy (SEM) revealed that stomata were sunken in the epidermis. We observed the non-contiguous stomatal cluster of abnormal stomatal pattern in six populations. We provide illustrations for all the reported stomatal types.