Whorled Wonders

Great Plains Ladies Tresses

The spiral, which is a fundamental form in nature, is most splendidly illustrated in a genus of wild, native orchids called Spiranthes.  Commonly known as ladies tresses, the genus name comes from the Greek speira meaning ‘coil’ and anthos meaning ‘flower’, and refers to each species spirally arranged inflorescence.  The most predominant species of orchid found in Texas prairies, several members of this genus are colonizers of sparsely vegetated areas, appearing on newly disturbed sites such as roadsides and cleared fields, increasing in number until outcompeted by other vegetation.

Of the 15 native Spiranthes species in Texas, several are so similar in appearance that either a hand lens or microscope is often needed to distinguish one from another. To add to the confusion, many closely related species are also known to hybridize. However, Central Texas, the most common include the Great Plains Ladies Tresses (S. magnicamporum) and the Nodding Ladies Tresses (S. cernua).  

Great Plains Ladies Tresses has 2 to 4 narrow, grass-like basal leaves, up to 6 inches long, that are usually absent or withering during the flowering period.  The flower spike can range from 4 to 24 inches tall, and is made up of 12 to 54 small white tubular fragrant flowers, tightly or loosely spiraled, that nod abruptly from the base.  Blooming from September to November, it prefers calcareous grassland habitat, often growing in association with our native Seep Muhly.  In wet years, this orchid may appear in robust spikes numbering in the hundreds, and in dry years it may not flower at all.

Nodding Ladies Tresses has 3 to 5 narrow, grass-like, basal leaves, 8 to 10 inches long, and are typically present at flowering.  It has a flower spike that can grow from 4 to 19 inches tall, and consists of 10 to 50 small white tubular flowers, tightly or loosely whorled in 2 to 4 rows along the upper portion of the stem.  Blooming from late September through November (and sometimes even into December), it can grow on wet or dry sites, but prefers more acidic, sandy soils.

Flowers of Spiranthes orchids begin opening at the bottom of the inflorescence.

Like most orchids, the flowers of these Spiranthes species are resupinate, or twisting during development into an upside-down position.  In fact, the tendency of the flowers to droop slightly gives the Nodding Ladies Tresses both its common and species name, for cernua comes from the Latin and means ‘drooping.’  Unlike other closely related species, the flowers of the Nodding Ladies Tresses have little or no fragrance, but like other closely related species, the flowers are pollinated by bumblebees.  As with most Spiranthes, bumblebees start at the bottom and move upward on the inflorescence in search of nectar. Older flowers at the base of the flower stalk have more nectar, which makes them an efficient first stop for the foraging bumblebees.

As mentioned above, many Spiranthes are difficult to identify to species, and both the Great Plains Ladies Tresses and the Nodding Ladies Tresses are no exceptions.  In fact, Nodding Ladies Tresses is known as a compilospecies, which is defined as a genetically aggressive species that incorporates the heredities of a closely related species by hybridization through unidirectional gene flow, and may even completely subsume that species over time.  Now that’s a whorled wonder!

Silent Flight

Eastern Screech-Owl

Owls have fascinated man from time immemorial – to some cultures they are symbols of wisdom, while to others they are harbingers of doom and death.  Adding to the mystique of these creatures is that they are mainly active at night, using their exceptional vision, acute hearing, and silent flight to stealthily hunt down their prey.

Common in Central Texas, the Eastern Screech-Owl is found in wooded suburban and rural areas and readily nests in tree cavities as well as man-made nest boxes.  A small owl 6-10” long with a wingspan of 19-24”, it has feathered ear tufts and is normally gray, brownish-gray, or less commonly reddish-brown.  The Eastern Screech-Owl eats a variety of small animals, and each night consumes from one-quarter to one-third of its own body weight.  It uses a soft trilling call to keep in contact with a mate or family members, and the male’s trill can advertise a nest site when courting a female or signal an arrival at the nest with food.  This owl also has a descending whinny, which is used to defend its territory.  Eastern Screech-Owl pairs are usually monogamous and remain together for life, although they will take a new mate when one dies.  In mid-April, the female lays 3-4 eggs on average, and the downy white owlets emerge from the nest by mid-May.

Great Horned Owl

Also common but much larger at 18-25” long with a wingspan of 40-57”, the Great Horned Owl prefers habitats of secondary-growth woodlands mixed with open meadows.  Often found perching next to an open area and nests in tree hollows, broken off snags, or nests made by other large birds.  It has prominent ear tufts spaced widely on its head, a brownish-gray body with dark barring, and a rusty facial disk edged in black surrounding each of its orange-yellow eyes. The Great Horned Owl has a broad diet of small mammals, birds, amphibians, and reptiles, and is the only animal the regularly eats skunks.  They have a large repertoire of sounds, but the most common is that of the male’s resonant territorial call ‘hoo-hoo hoooooo hoo-hoo’ that can be heard over several miles through the canyons on a still night. These owls are solitary in nature, only staying with their mate during the nesting season of January and February. Typically 2-4 eggs are laid and incubated solely by the female, until the young start roaming from the nest six to seven weeks later.  

The structure of an owl’s feather is the main reason they can fly so silently.  The leading edge of their primary wing feathers are serrated like a comb, which breaks down the turbulence into smaller, micro-turbulences.  The soft, tattered edges of their secondary feathers allow those small currents of air to pass through them and further reduce the turbulence behind their wings.  In addition, the velvety down feathers found in the wing linings and on their legs further dampen and absorb sound frequencies.  Together, these features allow the owl to greatly reduce the overall noise caused by the turbulence of air flowing over them as they fly.