Threatened species of Xanthophyta

This is a moderately small group of algae with about 100 genera and 600 species. They are primarily freshwater or soil algae; a few are marine. Typically they are rare algae and found in low abundance, although a few genera, including Tribonema and Vaucheria are reasonably common.

The taxonomy is unclear with different treatments according to the author. Some place the class Xanthophyta in the Heterokontophyta and others in Phytophyta (the larger grouping of algae).