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Why does Zelkova have a discontinuous geographic distribution?
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Rosales
Red garden roses (Rosa hybrid). Whereas wild roses have only five petals, most hybrid varieties have been bred to produce numerous petals in a wide range of colours.
The genus Zelkova exhibits a discontinuous geographic distribution because its historical range was significantly broader than its current one.1
Dating back to the beginning of the Paleogene Period, approximately 65.5 million years ago, the genus was much more widespread, with its presence confirmed by the fossil record across Eurasia and North America. Over time, however, environmental factors—specifically shifts in climate and the advancement of glaciers across the Northern Hemisphere—led to the elimination of Zelkova from many of these regions. Consequently, the genus now persists only in specific, separated areas, ranging from the eastern Mediterranean and the Caucasus to parts of East Asia.1