About Cerastium nigrescens (H.C.Watson) Edmondston ex H.C.Watson
Cerastium nigrescens var. nigrescens, commonly known as the Shetland mouse-ear, Shetland mouse-eared chickweed or Edmondston's chickweed, is an endemic variety of Cerastium nigrescens (Arctic chickweed) found in Shetland, Scotland. It was first recorded in 1837 by 12-year-old botanist Thomas Edmondston. While it was reported from two other sites during the 19th century, it currently grows only on two serpentine hills on the island of Unst, one of which is Keen of Hamar. The total population size of Cerastium nigrescens var. nigrescens can vary dramatically from year to year for reasons that are not fully understood; this variation is likely caused by changing rates of seedling germination and survival. The overall long-term population trend appears stable, and no changes to the variety's distribution have been observed. Mature plants of this taxon range from just a single shoot bearing one flower, to a fist-sized cushion that can hold as many as 40 flowers. The flowers are disproportionately large relative to the overall size of the plant.
