Betula uber Betula uber Betula uber, Virginia round-leaf birch, is a rare species of tree in the birch family. One of the most endangered species of North American trees, it is endemic to Smyth County, in the U.S. state of Virginia. It is part of the temperate broadleaf and mixed forests biome. The tree was first described in 1918 as a variety of "Betula lenta", and elevated to species status in 1945. It hybridizes with "B. lenta" and it has been suggested that it is actually a round-leaved mutant form of "B. lenta". Some authorities prefer to treat it as a variety.
Citrus gummy bark viroid observed in longitudinal sections. Citrus gummy bark viroid The citrus gummy bark viroid (abbreviated CGBVd) is a sub-species of the hop stunt viroid, and thus is a member of the genus Hostuviroid. As the name suggests, the citrus gummy bark viroid causes problems in the bark of the sweet orange tree. Scrapping the bark exposes localized spots or a line of reddish-brown, gum-impregnated tissue around the scion circumference especially visible near the bud union. The discoloration and gumming may extend above the bud union to the main branches of the sweet orange while in severe infection dark streaks of gum-impregnated