Redwood. Sequoioideae, popularly known as redwoods, is a subfamily of coniferous trees within the family Cupressaceae. It includes the largest and tallest trees in the world. The three redwood subfamily genera are Sequoia from coastal California and Oregon, Sequoiadendron from California's Sierra Nevada, and Metasequoia in China. The redwood species contains the largest and tallest trees in the world. These trees can live for thousands of years. Threats include: logging, fire suppression, climate change, illegal marijuana cultivation, and burl poaching. Only two of the genera, Sequoia and Sequoiadendron, are known for massive trees. Trees of Metasequoia, from the single living species Metasequoia glyptostroboides, are much smaller. Multiple studies of both morphological and molecular characters have strongly supported the assertion that the Sequoioideae are monophyletic. Most modern phylogenies place Sequoia as sister to Sequoiadendron and Metasequoia as the out-group. However, Yang et al. went on to investigate the origin of a peculiar genetic artifact of the Sequoioideae, the polyploidy of Sequoia, and generated a notable exception that calls into question the specifics of this relative consensus. Reticulate evolution refers to origination of a taxon through merging of ancestor lineages. Polyploidy has come to be understood as quite common in plants, with estimates ranging from 47% to 100% of flowering plants and extant ferns having derived from ancient polyploidy. Within the gymnosperms however it is quite rare. Sequoia sempervirens is hexaploid. To investigate the origins of this polyploidy Yang et al. used two single copy nuclear genes, LFY and NLY, to generate phylogenetic trees. Other researchers have had success with these genes in similar studies on different taxa. Several hypotheses have been proposed to explain the origin of Sequoia's polyploidy: allopolyploidy by hybridization between Metasequoia and some probably extinct taxodiaceous plant; Metasequoia and Sequoiadendron, or ancestors of the two genera, as the parental species of Sequoia; and autohexaploidy, autoallohexaploidy, or segmental allohexaploidy. Yang et al. found that Sequoia was clustered with Metasequoia in the tree generated using the LFY gene, but with Sequoiadendron in the tree generated with the NLY gene.