Pollen Identification on the Plant Origins of Houpo and Four Related Species

We observed the basic features of pollens from Magnolia officinalis Rehd. et Wils. and M. officinalis Rehd. et Wils. var. biloba Rehd. et Wils. (two botanical origins of Chinese Materia Medica Houpo) and related species of Magnolia Linnaeus (i.e. M. denudata Desr., M. liliiflora Desr., M. biondii Pampan. and M. grandiflora L.). We employed three methods for treating pollen samples of the six species, observed and compared their pollen morphology, surface ornamentation, and pollen size via scanning electron microscopy. Results indicated that the morphology from the side view, equatorial view, and polar view were quite similar among the studied species. The point ornamentation was small and shallow in Magnolia officinalis, and small but deep in M. officinalis var. biloba. Conversely, pollens from the other four species had obvious deep points and irregular uplifts over the surface. Pollen size ranged from large to small in the following order:Magnolia grandiflora,M. officinalis var. biloba,M. officinalis,M. denudata,M. liliiflora, and M. biondii. Here, the natural drying method outperformed the glutaraldehyde fixing method and the tert-butyl alcohol vacuum freeze drying method in describing the pollen morphology, surface ornamentation, and pollen size. The current research provides novel evidence for the identification of the origins of Chinese Materia Medica Houpo, and benefits further investigation on the lineages of Magnolia officinalis,M. officinalis var. biloba and their related species.