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Reduced Poaceae pollen under conditions of severe summer drought in the Middle East: Implications for rainfall seasonality in pollen diagrams

El-Moslimany, Ann
Review of palaeobotany and palynology 2019
Amaranthaceae, Artemisia, Pleistocene epoch, Poaceae, annuals, asexual reproduction, autumn, cleistogamy, drought, drought tolerance, flowering, grasses, perennials, pollen, rain, seeds, selfing, summer, Iraq, Middle East
Based on the facts that the Poaceae, in general, require summer precipitation, and that Artemisia and many Chenopods thrive in conditions of 4 summer drought, I have previously attributed the rise in grass pollen at the expense of Artemisia and Chenopodiaceae in Middle Eastern pollen diagrams at the end of the Pleistocene to a period of summer precipitation.Here, using present-day Iraq as an example, I assemble ecological and physiological information providing additional support for minimal Poaceae pollen release under conditions of summer drought, including: (1) dominance of the annual life-form over the usual perennials due to their ability to survive the summer as drought-resistant seeds and their ability to grow rapidly in the autumn, (2) abbreviated flowering of the annuals, (3) increased self-fertilization, including cleistogamy, in both annuals and perennials, and (4) the prevalence of vegetative reproduction, including apomixes, in the perennials.