Helianthus devernii

Helianthus devernii
Side view of the flower
Conservation status
Critically Imperiled  (NatureServe)
Scientific classification
Kingdom:	Plantae
Clade:	Tracheophytes
Clade:	Angiosperms
Clade:	Eudicots
Clade:	Asterids
Order:	Asterales
Family:	Asteraceae
Genus:	Helianthus
Species:	H. devernii
Binomial name
Helianthus devernii T.M.Draper

Helianthus devernii is a North American species of flowering plant in the Asteraceae family, known by the common name Red Rock sunflower. It is noted for its small area of distribution—less than 1 square acre.

Description

Helianthus devernii is a herbaceous plant with a perennial habit that regrows each year from an underground branched woody structure atop its roots. The stems reach as much as 102 centimeters in height and lack hairs but have a waxy coating making the surface somewhat whitish. Bone white stems from previous years are persistent and intermingle with the present year's stems.

The leaves are attached to the stems directly without a short leaf stem. Each leaf has one prominent vein or nerve, though lower leaves may have two additional indistinct veins. Leaf edges do not have teeth and the lower leaves are attached in pairs on opposite sides of the stems. The leaves nearer the midpoint of the stems are largest measuring 6.8–10.3 centimeters long and usually just 2.8–7.6 millimeters but occasionally as much as 10.3 mm. They have a very narrow, almost grass-like leaf shape but with gently curved sides. Lower leaves of Helianthus devernii have the same shape, but are shorter, 4.1–5.6 cm long and 4.4–9.0 mm wide, and are usually shed by the time the plant flowers. Leaves get shorter and thinner further up the stems ranging from 2.6–6.4 cm, though usually shorter than 5.1 cm, and just 1.2–1.7 mm wide with a very thin and grass like shape. The leaves also alternate rather than being opposite each other higher up on the plant.

The apparent flower is, as with most sunflowers, made up of many small flowers packed together into one head. Stems frequently end in just one flowering head, but sometimes will branch with a head at the end of each one. The petals of the ray flowers are yellow and 7.3–10.7 millimeters long, but usually longer than 9.0 mm. They are also 3.8–5.0 mm wide and have three teeth at the ends. There are five to eight ray flower around the twelve to twenty-eight disk flowers.

The seeds, technically called cypselae, are 3.5–4.0 millimeters long and have four sides. They are colored tan with darker brown specks.

Helianthus devernii can be distinguished from its close relative that also grows in Nevada, Helianthus cusickii because it has leaves that have just one prominent vein where H. cusickii has three. When blooming H. cusickii also has flower petals that are longer than 20 mm where H. devernii generally has petals shorter than 10 mm.

Taxonomy

In 2007, a researcher was conducting botanical surveys throughout the Spring Mountains in Nevada. The botanist did not recognize the plant, and it was not possible to use a dichotomous key because the inflorescences were too young. The botanist returned several weeks later when the plant was in a more advance phenology, but was unable to make a positive identification using regional floras. The plant was brought to Dr. Wesley Niles at the University of Nevada, Las Vegas but he, too, failed to make a positive identification. Another collection was sent to Dr. Edward Schilling at the University of Tennessee, who first suggested pursuance of a potentially new species. The first spring, second spring, and third southern cluster cover 800 square meters, 1800 square meters, and 4 square meters, respectively. Helianthus devernii was scientifically described as a species in a paper written by Trent M. Draper that was published in 2021. He selected the name to honor his grandfather, DeVern Campkin, for encouraging a love of science, history and geography. Genetic data indicates that it is most closely related to Helianthus pumilus, another sunflower species in section Ciliares.

As of 2024 it is an accepted species according to Plants of the World Online and World Plants, but is listed as "unchecked" by World Flora Online. U.S. Bureau of Land Management (BLM) refers to Helianthus devernii as the Calico Basin sunflower.

Distribution and habitat

Helianthus devernii, a rare endemic species blooming in Clark County, Nevada

The perennial herb is found within and around a small portion of Red Rock Canyon National Conservation Area in Clark County, Nevada—a BLM-managed National Conservation Area within the Mojave Desert. Part of the population occupies a named spring, but the majority grow in the riparian area created from well directly north of the spring. The Red Rock sunflower appears to require water in order to grow successfully, although it tends to occupy the dry upland area directly adjacent to the riparian area. The springs are within low-elevation desert scrub.

Original counts put the total number of individuals at around 400. Further surveys increased the total known number of individual plants to 725.

Conservation

The plant is critically imperiled due of its limited range and the threats in the area, which is a site of recreation, both legal and illegal. The latter includes equestrian use and off-trail hiking. Because of the recreational activities, noxious and invasive weeds are prevalent in the area, including Brassica tournefortii, Salsola tragus, Schismus spp. Invasive animals, like the burro, also threaten the plant.

A meeting to petition having the plant state-listed as a threatened and endangered species will occur in June 2024. While there are currently mitigation and management strategies underway, the results of this meeting will dictate the future direction for the conservation of the species.

Gallery

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  Flowering head, front view
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  Alternate leaves on Helianthus devernii
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  Flowering head, side view