Amborella trichopoda is a rare tropical understory tree endemic to New Caledonia, a small island about 750 miles off the coast of Australia in the South Pacific Ocean. As the only living species on the sister lineage to all other living flowering plants (angiosperms), Amborella represents an important reference for studying plant evolution.
As an early-diverging "basal" angiosperm, Amborella exhibits a number of noteworthy morphological features. For example, Amborella does not posses vessel elements for water conduction as do virtually all other flowering plants. The plant is dioecious (with separate male and female plants) and has small flowers with spirally arranged parts. The flowers possess an undifferentiated perianth of tepals (petal-like organs). For male flowers there are 9-11 tepals, and 11-22 stamens (which carry pollen); for female flowers, 5-8 tepals, zero to several staminodes (sterile stamens), and four to six carpels (which eventually become fruits). There is a developmental transition between leaf-like bracts and perianth, perianth and stamens, and between stamens and carpels. The stamens are laminar (leaf-like) and the carpels are sealed by a secretion of sticky fluid, rather than developmentally fused as in most angiosperms. The fruit is a red berry containing a single seed. Amborella has leaves that are alternately arranged, evergreen, and simple, with slightly serrated margins.
Amborella has a relatively compact genome among basal angiosperms (about 870 million base pairs organized in 13 chromosome pairs) and does not show evidence of recent genome duplication. As such, this basal-most angiosperm is ideal to root genomic comparisons of monocots and eudicots. The Amborella genome will provide key evidence to understand the ancestral state for every gene, gene family, and protein sequence in flowering plants, and how they radiated through the history of flowering plants. Gene clusters shared with other angiosperms provide direct evidence of ancestral genome structures and ancestral linkage groups, all of which could help understand economic plants and important plant processes. Amborella will facilitate understanding the ancestral radiation of gene families and transposable elements, provide insight into the extraordinary genetic processes that have led to frequent horizontal gene transfers involving mitochondrial, but apparently not nuclear gene sequences. Because of its unique phylogenetic position and relatively simple genome structure, an Amborella reference genome will aid researchers studying all aspects of angiosperm biology.
Read more about Amborella at the Plants of New Caledonia website.
Photo credits: Male flowers (left) by Joel McNeal; female inflorescence (right) by Sangtae Kim. Used with permission.