Winteraceae is a primitive family of tropical trees and shrubs including 93 species in five genera. It is of particular interest because it is such a primitive angiosperm family, distantly related to Magnoliaceae, though it has a much more southern distribution. Plants in this family grow mostly in the southern hemisphere, and have been found in tropical to temperate climate regions of Malesia, Oceania, eastern Australia, New Zealand, Madagascar and the Neotropics,

This family has been estimated to be anywhere from 105 to at least 35 million years ago. Being one of few angiosperms forming persistent tetrads with prominent sculpturing, pollen of Winteraceae is rare but easy to identify in the fossil record. but the association of these fossils with Winteraceae is uncertain. Equally characteristic is Winteraceae wood, which lacks xylem vessels in contrast to most other flowering plants. western North America (Central Valley, California; Maastrichian) and Europe (Helmstedt, Germany; Eocene).

According to the 1998 APG I system, it did not belong to any order, but it has since been placed in Canellales by the APG II, APG III and APG IV systems.

Description

Members of the family Winteraceae are trees or shrubs. The leaves are alternate, with light green dots and a fragrant aroma. Some are used to produce essential oils. Stipules are absent. Flowers are small, mostly appearing in cymes or fascicles. They have two to six free, valvate sepals, though they are united in Drimys. This makes them relatively immune to xylem embolisms caused by freezing temperatures. In addition, vascular occlusion can occur near the openings of the stomata, preventing excess water from entering.

Evolution of vesselless wood

Winteraceae was initially placed as a basal group within the Angiosperms due to its vesselless wood. Xylem vessels were seen as an important evolved character for the diversification and success of Angiosperms, so vesselless wood was seen as an archaic trait, resulting in basal placement of the Winteraceae. However, molecular phylogenetic work placed Winteraceae within the Magnoliids, well within the angiosperms. This meant movement from hot humid environments to temperate humid environments where freeze-thaw events occurred. Vesselless wood has 20% of the water conductivity of vessel-bearing wood, however, under freeze events, wood with vessels loses up to 85% of water conductivity while vesselless wood loses at most 6% of water conductivity. This movement from hot humid environments to temperature humid environments where freeze-thaw events occurred is seen as the evolutionary pressure behind the unique reversion to vesselless wood in Winteraceae.

Another character of Winteraceae that was seen to indicate a basal position in the phylogeny was the presence of waxy stomatal plugs, seen as limiting water loss in respiration and therefore an archaic trait to limit water loss. However, further research showed that in these humid environments, water cover on the surface of leaves decreased photosynthetic rates and waxy stomatal plugs reduce this water cover and therefore reduce the negative impacts on photosynthetic ability. Winteraceae species with stomatal plugs removed saw decreases in photosynethic rates of up to 40%.

Notable species

Drimys winteri (Winter's bark) is a slender tree native to the Magellanic and Valdivian temperate forests of Chile and Argentina. It is a common garden plant grown for its fragrant mahogany-red bark, bright-green leaves, and its clusters of creamy white, jasmine-scented flowers. The bark has historically been used to prevent scurvy.

Tasmannia piperita is notable for the great range of numbers for petal, stamen and pistil counts. Tasmannia lanceolata, known as Tasmanian pepper, is grown as an ornamental shrub, and is increasingly being used as a condiment.

References

  • Chilean Winteraceae Chileflora