Dwarf Palmetto, Sabal minor

Thursday, August 6, 2009

Nature Notes
by Bob Thomas

The most visible indicator species of bottomland hardwood forests in south Louisiana is the understory-growing, shade-loving dwarf palmetto (Sabal minor). Although its densest growths are usually found in such habitats, it is often found spottily distributed along natural levees. They are distributed throughout the southeastern United States excepting most of peninsula Florida. In Louisiana, they are found statewide, but are most abundant in the southern half of the state.

The evergreen leaves of the dwarf palmetto are bluish-green and consist of an unarmed--meaning they have no thorn-like projections--leaf stalk (petiole) and a fan-shaped (costapalmate) assortment of about 20 long blades. The petioles may be up to three feet long; the fan ranges in size from one to five feet in diameter. Each of the blades has a central rib.

There are two growth forms of dwarf palmettos. The most widespread is called acaulescent--meaning the stem is completely underground--so the leaves appear to arise from the roots in the soil. This growth form is presumably an adaptation that protects them from fires in their habitat.

The other type is caulescent--or with a trunk. In the Bayou LaBranche area, there are trunked palmettos that reach heights of six feet or more. A specimen eight feet, eight inches tall was reported from Frenier Beach north of Bayou LaBranche's mouth on the west end of Lake Pontchartrain. Records of these plants in Brazoria County, Texas, reaching over 20 feet are now thought to be based on hybrid specimens.

The caulescent palmettos are possibly a growth response originating in specimens growing in crevasse zones along the Mississippi River. According to Tyrone Forman, renowned local wetlands naturalist, the theory is that, as they were covered with alluvial soils as the river poured over their habitat, the stems continued to grow upward. Over time, the soil subsided around their bases leaving an exposed trunk. As they continued to add leaves (about three per year), they continued to grow higher ever so slowly.

This growth habit led Native Americans and early settlers to consider the habitat of this stalked form to be high ground--above the normal flood line.

The caulescent growth form was once considered to be the distinct species Sabal deeringiana. Today, we know it to be simply a growth form of Sabal minor.

Dwarf palmettos have clusters of small, monoecious (each having both male and female structures) white flowers on stalks that extend higher than the leaves. After flowering between late spring and midsummer, the ripening fruit are black, hard spheres less than one-half inch in diameter.

In his 1945 Louisiana Trees and Shrubs, the late Dr. Clair Brown gives the following economic values for the species: roof thatching, source of fibers, and a producer of honey. We know that at least nine species of birds feed on their berries, as well as mammals such as opossums and raccoons.

The trunked form of palmettos take many years to grow, and they can be inadvertently killed in moments. Tyrone Forman is deeply concerned that these wetland treasures will be killed by people who don't know their natural and scientific value. "Palmettos photosynthesize through their leaves. If they are cut for such purposes as basket making, thatching roofs, or building duck blinds, the result may be the death of a 250-year-old natural treasure," he says.

Forman asserts that the national champion dwarf palmetto may well be standing in the LaBranche Wetlands. That would certainly be another natural feather in the cap of ecotourism for the Lake Pontchartrain Basin and Louisiana.

                                          

Classic view of dwarf palmetto, Sabal minor,                                Famed naturalist Milton Cambre with a
in the understory of a bottomland hardwoods                              caulescent (trunked) dwarf palmetto.
habitat.                                                                                    Photo by Bob Thomas.
Photo by Bob Thomas.

Dwarf palmetto with fruit.
Photo by Bob Thomas.