[Pollen of gramineae and its botanical, taxonomical, and ecological aspects]

This is a review of tropical pollens (Gramineae) which cause allergy, addressed to medical workers and with emphasis in the Costa Rican. The graminean family Poaceae is widely distributed and has great genetic plasticity. An evolutionary tendency to floral reduction has led to anemophily, with pollens ranging from large (e.g. corn, Zea mays) to very small (e.g. tribes Poae and Avenae). This family produces a large number of pollens per panicle. The early morning production of free pollen (before 8 am) enhances allergic problems. In contrast, in rice (Oryza sativa) most pollen is liberated near mid day, which favours long range dispersal because of more appropriate environmental temperature and humidity. This can explain why rice is the first cause of allergic sensitivization in the asthmatic patients of the Costa Rican driest provinces (Guanacaste and Puntarenas). Despite the small size of several temperate and tropical species are present, because of geographic position, climatic diversity, irregular topography, etc. This paper presents a general description of the subfamilies Pooideae, Panicoideae, Chlorideae (Eragrostoideae) and Oryzoideae (including the medically most important tribes). Their pollens are illustrated with light and electron microscopy.