MONDAY, 25 SEPTEMBER 2023Mountains all over the world are known as biodiversity hotspots. New Zealand’s largest group of endemic (native) plants, flowering shrubs called hebes (genus Veronica), has over 120 species. Most species live in mountain habitats in New Zealand’s Southern Alps. DNA evidence suggests the group is only around 6 million years old — relatively young on an evolutionary timescale — but hebes have surprisingly diverse forms. They range from small trees with long, narrow leaves, to dense shrubs, to cushion plants that only grow in the high alpine zone. Can their preferred mountain habitats explain how hebes evolved so much diversity in so little time?
Although the estimated origins of the hebes predate the uplifting of the Southern Alps (also quite young mountains), models simulating how species may have evolved and migrated over time suggest that once uplifting began, a few ancestral lowland species colonised the growing mountains. Once there, populations encountered barriers created by rocky cliffs and fluctuating glaciers, as well as opportunities to adapt to new alpine environments by taking on new forms. Forces like this may have encouraged the burst of diversification that gave rise to the species living there today. But without a time machine, we’ll never know for sure exactly what went on in the Southern Alps during those millions of years!
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