Pollen morphology and taxonomy in North American Labiatae

Pollen morphology is described and illustrated based on SEM studies of 118 species of Labiatae (Lamiaceae) native to North America. These include representatives of all the 36 native genera. Pollen in this family is subspheroidal and either tricolpate (subfamily Lamioideae) or hexacolpate (subfamily Nepetoideae). In most of the genera and species, the tectum is conspicuously perforated with or without a supratectal reticulum. A key to facilitate identification of the pollen of the North American Labiatae is provided. The value of pollen as a taxonomic character in this family is discussed. Pollen provides the primary basis for recognition of subfamilies in the Labiatae, but at the tribal level only the Ajugeae has distinctive pollen. Several genera, notably Collinsonia, Salvia, Teucrium, and Trichostema, have pollen that is very different from other genera in this study. At the infrageneric level pollen provides valuable taxonomic characters in several genera, notably Hyptis, Monardella, Salvia, Stachys, Teucrium, and Trichostema.