What type of category does Echium and Oxydendrum have in common?
Echium Echium is a genus of 60 species of flowering plant in the family Boraginaceae.
Isoetales Isoetales, formerly also written Isoëtales, is an order of plants in the class Isoetopsida. There are about 140-150 living species, all of which are classified in the genus "Isoetes" (quillworts), with a cosmopolitan distribution, but often scarce to rare. Living species are mostly aquatic or semi-aquatic, and are found in clear ponds and slowly moving streams. Each leaf is slender and broadens downward to a swollen base up to 5 mm wide where the leaves attach in clusters to a bulb-like, underground corm characteristic of most quillworts. This swollen base also contains male and female sporangia, protected by a thin, transparent covering (velum), which is used diagnostically to help identify quillwort species. Quillwort species are very difficult to distinguish by general appearance. The best way to identify them is by examining the megaspores under a microscope.