Pollen Grain Studies of the Labiatae of Michigan

SUMMARY Pollen grain studies have been made of 50 species of the Labiatae occurring naturally in Michigan and of 5 cultivated species. The characteristics of pollen grain morphology are discussed and are also summarized in a table. For a number of species, a determination has been made of nuclear content of pollen grains at anthesis. Two major morphological groups of grains have been recognized: those that are binucleate and tricolpate and those that are trinucleate and hexacolpate. This observation confirms a previous report of this condition. Variation in size and increase in number of colpi within individual plant specimens have been observed in 5 naturally occurring species. Comparaisons have been made of untreated plants with a cultivar which was irradiated or treated with colchicine. Pollen grains with more than 6 colpi also have been found to be trinucleate. A key to 49 species (based on acetylated pollen grains) has been constructed.