Pollen morphology of Magnolioideae in China and its taxonomic implications

• The fresh pollen grains in Magnolioideae were investigated by SEM.
• Microgemmae on the tectum surface of pollen grains were found for the first time.
• Micromorphological characters of pollen grains were quantified.
• Six pollen types and three subtypes are proposed in the Magnoliaceae.
• Magnolioideae should be divided into small genera, but not a single genus, Magnolia.

Fresh pollen grains of 37 species representing eight genera (Magnolia, Manglietia, Lirianthe, Houpoëa, Talauma, Michelia, Woonyoungia, and Parakmeria) of the subfamily Magnolioideae, one of the most primitive families among the angiosperms, were investigated using scanning electron microscopy, and 31 of them are reported for the first time. The Magnoliaceae family is typically stenopalynous. Pollen grains are bilaterally symmetrical, heteropolar, boat-shaped and monosulcate, rounded or elliptical in distal view. They are medium to large in size, ranging from 41.6 ± 4.4 μm to 94.1 ± 5.6 μm in the longest axis. Most species examined have microperforate ornamentation. Uniform perforations of 0.2 μm or from 0.1 μm to 0.5 μm in diameter on the outer surface of the exine were detected in Manglietia and Lirianthe species. Pollen grains of some species had microgemmae or ring-like appurtenances on the outer surface of the exine. Six pollen types and three subtypes are proposed in the Magnoliaceae. This is one more than the five types proposed by Praglowski in 1974. A key for the identification of these pollen types and subtypes is presented and its taxonomic implications in the Magnolioideae are discussed.