Friday, February 27, 2015

Protea and its Cousins

Protea cynaroides in flower at the UConn greenhouses, late winter.
Protea is a genus of about 90 species of leathery shrubs, mostly confined to South Africa and definitely at its most diverse in the fynbos, a scrubby vegetation type that develops on poor soils in winter-rainfall, mediterranean-type climatic areas in the general vicinity of Cape Town. Proteas are known for their often spectacular flowers, which are actually not single flowers but clusters of hundreds of individual florets surrounded by showy bracts (modified leaves). Protea cynaroides, the national flower of South Africa, has some of the showiest inflorescences in the genus, easily a foot across from powdery pink bract tip to bract tip.

Proteas are mostly found in habitats that experience wild fires on a regular basis, perhaps every 10 to 30 years. Unlike some fynbos plants, most proteas have no special ability to survive fire, and instead rely on regeneration from seed. Protea seed heads are tough structures that persist at the tips of branches for years, only opening to spread their seeds after their parent plant has been incinerated. Seed germination is triggered by chemicals in smoke. Protea cynaroides is one of the few species where mature plants can live through fires; they regenerate from buds on a swollen stem at the base of the plant.
Proteoid roots - Protea neriifolia
A characteristic of Protea and other genera in the family Proteaceae is the production of proteoid roots, highly branched bushy clumps of short roots. Proteoid roots are involved in the uptake of nutrients in impoverished soils, and similar structures have been described in representatives of other plant families that specialize in low-nutrient habitats.

Grevillea leucopteris in flower, late winter.
The family Proteaceae includes about 75 genera, centered in southern Africa, South America and Australia, with only a tentative toehold in the Northern Hemisphere in tropical Africa, Asia and Central America. Western Australia hosts a particularly diverse flora of Proteaceae, such as Grevillea leucopteris, pictured above, along with numerous other genera and species. The flowers of G. leucopteris emit a somewhat musty sweet smell, which has apparently earned the plant the unflattering common name "Old Socks."

The evolutionary relationships of the family Proteaceae were for a long time obscure and controversial: it seemed to be an isolated lineage without close living relatives. Modern DNA sequencing, coupled with improved mathematical techniques to reconstruct phylogenies (evolutionary trees), and the brute computer power to implement those techniques, has resolved a lot of old plant classification mysteries, including the placement of the Proteaeae. Protea and its relatives are now included in the order Proteales, along with the families Sabiaceae, Nelumbonaceae and Platanaceae.

Nelumbo nucifera, Sacred Lotus, in the outdoor pool by the Enid Haupt Conservatory at the New York Botanical Gardens, mid-summer.
Two of these are small, monogeneric families with only a few species, that will nonetheless be familiar to most readers: Nelumbonaceae is the family for Nelumbo, the lotuses, formerly sometimes considered to be allied to the water lilies (family Nymphaeaceae), which they superficially resemble. The Platanaceae includes the plane trees and the Sycamore, large north temperate trees with distinctive peeling bark. A plant order is a very broad taxonomic grouping, but I do not believe that any botanist had suspected that the Sacred Lotus, the common city park resident London Plane Tree, and the proteas would find themselves in the same order, prior to the ascendance of molecular phylogenetics. 

Young Platanus trees, probably P. x acerifolia (London Plane Tree), producing their first fruiting heads. Storrs, Connecticut, February.

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