Resilient Ruellias

Ruellias flower throughout the heat of summer.

Are you looking for native, non-aggressive flowering plants that are perfectly adapted to our central Texas limestone soils and extreme summer heat? Then look no further than some of our local species of Ruellia, also informally but incorrectly called wild petunias. They include Drummond’s Ruellia (Ruellia drummondiana), Hairy Ruellia  (Ruellia humilis), Metz’s Ruellia (Ruellia metziae), and Violet Ruellia (Ruellia nudiflora).

Drummond's Ruellia

A Texas endemic, Drummond’s Ruellia has ovate, fine-haired leaves and purple to dark lavender stalkless (sessile) blooms arising from the leaf axils (axillary). It is prominent on the Edwards Plateau and in and around Austin, and blooms from June to November. Hairy Ruellia, also called Fringeleaf Wild Petunia, has conspicuously hairy oval leaves with pointed tips and hairy margins, and purple to pale purple axillary, sessile blooms. It is highly drought-tolerant and is widespread in open prairies on limestone soil, where it blooms from May to September.

Hairy Ruellia

Metz's Ruellia

Metz’s Ruellia or White Ruellia is distinct in that it features uncommonly white or pale-throated stalked (peduncled) blooms in a branched structure (panicle) at the tops of stems (terminal), and oval leaves on long leaf bases (petioles). It thrives on limestone outcrops and in open woods, and blooms from June to August. Violet Ruellia, also called Common Wild Petunia, is one of the most ubiquitous of all these species, with a similar arrangement of peduncled blooms in a panicle on the terminal ends of stems, but the blooms are purple to violet-blue. The leaves are oval, smooth and essentially hairless (glabrous) with somewhat wavy margins, and the blooms occur from April to October.

Violet Ruellia

Mexican Petunia (non-native)

Unlike the invasive, non-native Mexican Petunia (Ruellia simplex) that is sold in many nurseries, these resilient native species are well-behaved. They provide a bounty of successive summer blooms while other flowering plants are wilting in the heat. Their flowers open in the morning and fall off by evening, and they can be correctly identified by the structure of the inflorescence (axillary or panicled), leaf texture (waxy, hairy, or fringe on margins) and leaf shape (ovate, oval, or lance-shaped). The Hairy Ruellia and Violet Ruellia species are also host plants for Common Buckeye and White Peacock butterflies.

The genus Ruellia was named after a French botanist and physician, Jean Ruelle, who lived during the Renaissance Period. He was noted for his 1536 publication in Paris of De Natura Stirpium, a Renaissance treatise on botany, which included detailed descriptions not only of a plant species' habit and habitat, but also the smell and taste of each.

Cooling Conduct

Eastern Ringtail dragonflies obelisking

The unrelenting heat this summer has affected all living creatures, and while humans can escape into air-conditioned spaces, wildlife needs to rely on other ways to regulate their body temperature.  Often this is accomplished through different types of behavioral strategies acquired through adaptation, and some may seem quite odd until you understand the dynamics at work.

One of the most obvious behaviors (for humans at least), is sweating.  But many creatures don’t have sweat glands, or only sweat from their feet (like some canines), so they rely on panting instead.  In panting, animals breathe rapidly and shallowly with their mouths open, thereby increasing evaporation from the surfaces of their mouths.  This evaporation removes heat and acts as a cooling mechanism.  Panting is used by most mammals (like dogs) and many species of birds. While panting is effective at removing heat, dehydration is a risk so a nearby water source is important.  Birds may also spread their wings and body feathers to allow heat to dispel, and they have an elaborate breathing system that includes air sacs (in addition to lungs) to help them get rid of excess heat through panting.

A molting Northern Cardinal, panting and spreading its wings to cool down

Some birds, such as some species of vultures and storks, will voluntarily defecate on their legs to cool down.  Since bird poop is mostly liquid, it works by having an evaporative cooling effect, much like sweating.  As the poop dries on the bird’s legs, the heat is carried away and it brings down their body temperature.  Pelicans, herons, doves, owls, quail, and nighthawks, can employ gular fluttering, vibrating the muscles and bones in the throat and exposing moist throat membranes to the air, which helps regulate temperature by increasing evaporation.

Insects, like most all creatures, can also maintain a stable body temperature in at least a portion of their bodies through some interesting behavioral means.  While many insects need some heat to warm up their flying muscles, many will adjust/reduce their activity levels or seek out shady spots to handle extreme heat.  Dragonflies, for example, will often obelisk while perched in the midday hot sun, or point the tip of their abdomen directly up at the sun.  It is believed that this behavior reduces the heating effect by reducing the amount of surface area exposed directly to the sun’s rays.

Checkered Setwing exhibiting obelisking as a cooling behavior

When temperatures soar, four-legged animals such as squirrels, marmots, rabbits, bears, and even dogs and cats will lie flat on their stomachs on a cooler surface with their arms and legs stretched out from their bodies.  This behavior is called splooting, and it is thought that since their bellies have less fur and lots of blood vessels, they can dissipate the heat and absorb some of the coolness from the surface.  Also known as frogging or pancaking, splooting can take on various forms: the full sploot (all four legs out), the classic sploot (one leg tucked underneath the body while the other is kicked back), the side sploot (one leg tucked under the body and the other kicked out to the side), and the reverse sploot or toolps (when the animal lays on its back with its legs in the air)!

Fox Squirrel in a full sploot on our back porch

Regardless of the method, we all have to find some form of cooling conduct that allows us to survive until temperatures fall and (hopefully) the rains begin once again.

 

Some Like It Hot

Eastern Ringtails, a type of Clubtail, obelisking.

The dog days of summer are upon us, and a long stretch of sultry weather lies ahead.  It can be a challenging time for people and for wildlife, but for some, it is their chance to put on a show. 

Bouquets of Mountain Pinks

Mountain Pink close up

Mountain Pink (Zeltnera beyrichii), also called Meadow Pink, Catchfly, or Quinineweed, is an annual herb less than a foot tall and best described as a neat bouquet of small, pink flowers.  Blooming May through July, Mountain Pink sprouts up like an inverted cone 8 to 12 inches high, on hot, rocky hillsides, limestone outcrops, and along gravelly roadways.  Its leaves are threadlike and are held below the multiple 0.5 to 1.0 inch wide showy pink five-petaled blooms that provide nectar for moths, butterflies, bees, and other insects.

Woolly Ironweed

Woolly Ironweed (Vernonia lindheimeri) is a 10 to 30 inch high clumping perennial, with woolly gray stems and long, narrow leaves.  Its bright purple flowers lack true petals, but the disk flowers are arranged in showy, terminal clusters.  A well-behaved species that should be used more often in gardens and landscapes, Woolly Ironweed blooms from June to September, and prefers open hillsides, roadsides, and fields offering full sun.  It is a good nectar source for many species of butterflies during the heat of summer, and is highly deer-resistant.

Blue Dasher, a type of Skimmer, obelisking

To prevent overheating on hot, summer days, some dragonflies and damselflies assume a handstand-like position called ‘obelisking.’  They raise their abdomens until the tip points up toward the sun, which helps to minimize the surface area of their body that is exposed to solar radiation.  Both males and females of these species will raise their abdomens when the temperature is high, and lower them again if shaded. Laboratory experiments have shown that this behavior is effective in stopping or slowing the rise in their body temperature.  This method of thermoregulation is practiced by about 30 different species in the Skimmer, Clubtail, and Broadwing Damsel families.  All are considered ‘perchers’ or sit-and-wait predators that spend a considerable amount of time stationary.

A sure sign that we are in the midst of a hot summer is the sound of cicadas buzzing in the air.  For their size, cicadas make as much noise as a large animal, and can be heard up to a quarter of a mile away.  In fact, the word ‘cicada’ is a direct derivation from the Latin meaning ‘buzzer.’  Many common species of cicadas in North America are in the genus Megatibicen  and are generally called the annual or ‘dog-day’ cicadas because they emerge every year in July and August, the dog days of summer.

Resh Cicada, Megatibicen resh

Male cicadas have structures called ‘timbals’ on the sides of their abdomens, and it is with these structures that they create their buzzy songs.  Unlike grasshoppers or crickets that rub their wings or legs together to produce sound, cicadas vibrate these timbals against their hollow abdomens, which amplifies the resonance of the sounds. They can even modulate the sounds by wiggling their abdomens toward or away from the tree trunk on which they are perched.  Each species has its own distinctive sound, and they use different mating songs to attract the appropriate mate.

Even in the heat of a long Texas summer, nature is busy going about its mysterious ways, offering sights and sounds that can recalibrate our senses, and allow us to continue to appreciate all that it has to offer.