The Rare Houston Camphor Daisy

As one of the 33 leading botanical gardens and arboreta in the United States, Mercer Arboretum & Botanic Gardens maintains the Houston Camphor Daisy, a rare Texas endemic (a native unique to one geographic area) wildflower for the Center of Plant Conservation’s National Collection of Endangered Plants.

The Houston Camphor Daisy was first described in 1849 as Haplopappus aureus by America’s leading botanist of the middle 19th century, Dr. Asa Gray, MD (1810-1888). Gray’s samples were collected in Harris County for the Harvard University Herbarium by his colleague, Charles Wright (1811-1885). Wright was a botanist and a principal alumnus of the first college in Texas, Methodist Rutersville College near La Grange. A "herbarium" refers to a collection of dried plant samples stored in a room or building for scientific study.

In 1950 the Houston Camphor Daisy was re-examined and named Machaeranthera aurea by Dr. Lloyd Herbert Shinners (1918-1971), director of the Southern Methodist University (SMU) Herbarium in Dallas. The Botanical Research Institute of Texas (BRIT) founded in 1987 in Fort Worth is now home to the Herbaria of SMU, BRIT and Vanderbilt’s Lloyd Shinners’ Collection in Systematic Botany. These herbaria contain a growing collection of nearly one million preserved botanical specimens and are named in honor of this famous Canadian-born, Texas botanist. The internationally recognized, botanical scientific journal, SIDA, Contributions to Botany, established in 1962 by Dr. Shinner also resides at BRIT.

In 1996, based on state-of-the-art genetic examinations of Machaeranthera and other related plants, the botanists, M.A. Lane and R.L. Hartman, removed the Houston Camphor Daisy from the Machaeranthera group and renamed this rare daisy "Rayjacksonia aurea." Botanist Dr. Raymond C. Jackson, an authority for the largest family of the higher plants, the Asteraceae, is honored in this name. Composed of approximately 21,000 members, the Asteraceae family is also called the Composite, Sunflower or Daisy family and occurs worldwide, except in Antarctica.

In the Composite family, blooms are typically arranged as a "head" composed of many small flowers attached to a base, the "receptacle." In many Composites, including the Houston Camphor Daisy, the outer or marginal flowers of the head have a single, showy, petal-like strap and are referred to as "ray flowers." The interior, tube-shaped flowers are called the "disc flowers." The "petal" of a Daisy is actually a petal-like strap from one individual ray flower. The ray flowers form a circle at the outer margin of the Daisy’s head and the many disc flowers form the center of the head. Common garden favorites including the Sunflowers, Aster species and Daisies are Composites that often display the ray and disc flower arrangement shown by Rayjacksonia aurea.

The Houston Camphor Daisy is a tap-rooted annual and grows to 20 inches tall. The branched stems bear elongated, smooth-edged or sparsely–toothed, one to two inch long leaves. The Latin word "aurea" used to describe Rayjacksonia aurea denotes the golden-yellow color of the ray and disc flowers.

The single seed produced from a fertile flower is enclosed within a dry, thin-shelled fruit named an "achene" or "cypsela". The fruits produced by the ray and disc flowers are crowded within each head of a Houston Camphor Daisy. Sunflower seeds are popular examples of the fruits formed by members of the Composite family.

The three annual herbs identified as Rayjacksonia occur only in North America, display yellow flowers and emit an aromatic camphor-like odor. The odor reportedly repels browsing deer. The common Camphor Daisy occurs in the Rio Grande and Gulf Coastal Plains, however, our rare Rayjacksonia aurea, occurs only in Harris and Galveston Counties and is a pioneer plant of barren soils.

Historically, the Houston Camphor Daisy occurs on "pimple mounds" or "mima mounds," natural bare spots in the native coastal prairies. The Houston Camphor Daisy is often associated with the rare Texas Windmill Grass, Chloris texensis and Prairie Dawn, Hymenoxys texana. Mercer also maintains the Texas Windmill Grass and Prairie Dawn for the National Collection of Endangered Plants.

Mercer’s conservation partners, local botanists Dr. Larry E. Brown of the Houston Community College and Spring Branch Science Center and Ralph J. Taylor of Harris County Flood Control District’s Environmental Services Department, collect seed stock and monitor local wild populations of Rayjacksonia aurea as well as other rare Harris County species for the National Collection of Endangered Plants. The rare Houston Camphor Daisy blooms in the fall and is displayed for the public in Mercer’s Endangered Species Garden.

Anita A. Tiller, Botanist, Mercer Arboretum & Botanic Gardens, Autumn 2001 

Photo by Greg Wieland