Pollen morphology inaloe(Aloaceae)

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Abstract
Pollen of two North American monotypic genera (Pterostegia and Harfordia) in the tribe Pterostegieae (including three varieties of Harfordia ca. 22 specimens in total) was examined with light microscope and scanning electron microscope. Detailed descriptions of the inner surface of the tectum and endoapertures were investigated using freezing microtome sections in SEM. The pollen of Pterostegieae can be characterized as being usually 3‐colporate, lolongate or almost circular (more common in Harfordia) and having endoapertures with a subtectate‐microreticulate or ruglo‐/striato‐perforate exine sculpturing. The pollen grains of Pterostegia and Harfordia are very much alike and are therefore, not easily separable, although there are some slight variations (especially in pollen size and sexine patterns, etc.). The infratectum of pollen in Harfordia is covered with comparatively few and less dense granules than that of Pterostegia and these characters are reported for Pterostegia drymarioides for the first time here. This palynological detail (i.e., granular inner tectum surface) might be considered an important synapomorphic character, which reinforces the concept of a close relationship between the tribes Pterostegieae and Eriogoneae in the subfamily Eriogonoideae.