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.

Saturday, February 7, 2015

Spanish Moss Cold Hardiness

Tillandsia usneoides grown outdoors in Connecticut and brought inside on December 24 (left) and January 12 (right).
 Tillandsia usneoides, or Spanish Moss, is a rootless epiphyte with inconspicuous greenish flowers, in the family Bromeliaceae (the pineapple or bromeliad family), and one of the emblematic plants of the American South. It is native to an enormous geographical range in the tropics and warm temperate regions of the New World, from coastal southeastern Virgina and possibly Maryland, down almost to the southern tip of South America in Argentina and Chile. The whitish appearance of the plants is the result of a dense coat of umbrella-shaped (peltate) hairs, which are involved in trapping and absorbing the rainwater and trace nutrients.

Tillandsia usneoides grows naturally in locations that experience considerable frost, and would appear to be the most cold hardy of the epiphytic angiosperms (flowering plants). I have grown Spanish Moss outdoors in the branches of trees in Mansfield, Connecticut many times and it always does quite well from spring to fall. Plants that are left out over the winter have never survived, though, even in mild years.

This winter I had left out a number of clumps of extra T. usneoides, but after they had been thoroughly frosted I decided to bring some in to the UConn greenhouse to see if they could be revived. Plants retrieved on December 24 looked a little dehydrated at first but recovered quickly in the greenhouse, with negligible die back. November-December was warmer than normal, but the plants had experienced numerous hard freezes, some multiple-day stretches of sub-freezing temperatures, and absolute lows of about 10°F (-12°C).

Another clump brought inside on January 12 experienced much harsher weather, including week long periods with daytime highs below freezing and absolute lows of -2°F (-19°C). Although this plant probably lost well over 90% of its shoots, a smattering of stem tips with a couple of leaves and internodes have definitely survived and are resuming growth in a cool but frost-free greenhouse. Still, the plant was clearly near the limits of survivable conditions.

Three different collections of Tillandsia usneoides: typical USA form, gathered in Charleston, SC by R.W.A. Opel (left); fine Carribean form from the Dominican Republic (center); robust form from Peru (right).
As might be expected from a plant with such a wide native range, T. usneoides is variable in appearance from place to place; the photo above shows three forms collected in different localities but grown in the same greenhouses. This year's hardiness tests were carried out with cultivated Spanish Moss originating in the southeastern USA; in previous years I have tried the Peruvian material outdoors, but it succumbed rapidly during the first hard frosts in autumn. So, there seems to be some genetic variability in winter hardiness in T. usneoides. It might be interesting to experiment with outdoor cultivation of material from the northern limits of the range of Spanish Moss, Virginia or the inland edges of the Carolina Low Country. Success would seem unlikely in Connecticut, regardless of the wild source of the plants, but I wonder if some adventurous gardener might be able to establish T. usneoides in a mild, protected coastal location in New Jersey or Long Island, or possibly even the more maritime parts of Massachusetts, say Martha's Vinyard or the Outer Cape.

Addendum: I rescued some more clumps of T. usneoides from outdoors in mid-February, after more extended periods of sub-freezing weather. Some shoots still looked pretty green initially, but this was the green of a package of frozen spinach; everything was clearly brown and dead a few days after thawing out.