| Croton alabamensis var. texensis | |
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Scientific classification  | |
| Kingdom: | Plantae |
| Clade: | Tracheophytes |
| Clade: | Angiosperms |
| Clade: | Eudicots |
| Clade: | Rosids |
| Order: | Malpighiales |
| Family: | Euphorbiaceae |
| Genus: | Croton |
| Species: | |
| Variety: | C. a. var. texensis |
| Trinomial name | |
| Croton alabamensis var. texensis Ginzbarg [2] | |
Croton alabamensis var. texensis is a variety of Croton alabamensis that is endemic to the state of Texas in the United States. It is commonly known as the Texabama croton.
Croton alabamensis var. texensis is a multi-stemmed, monoecious shrub typically less than 3 m in height at maturity. [3] Stems are covered in thin grey bark. The indumentum consists of unpigmented silver scales and pigmented copper-colored scales. New stems, petioles, leaf undersides, inflorescences, and floral parts have a coppery sheen because pigmented scales are present. [4] The plant is able to reproduce asexually through layering, eventually forming clonal colonies. [3] Plants are fire-tolerant and will resprout vigorously following wildfire. [5]
The simple, petiolate leaves are arranged spirally and are found at the ends of stems. Blades measure 3.8 to 9 cm in length and 1.5 to 4 cm in width, have entire margins, and are ovate to elliptic. The apex is acute, rounded, or emarginate, while the base is obtuse to slightly cordate. The tops of the leaves are dark green with scattered silver scales. [4] Leaf undersides are completely covered in scales, most of which are unpigmented, [6] and have prominent veins. [4] Although older leaves turn orange in the fall, [7] it is a semi-evergreen plant because the leaves are retained during mild winters. [8]
The inflorescence is a terminal raceme with 6 to 14 inconspicuous flowers formed on buds from the previous year. Racemes have 1 to 6 pistillate (female) flowers near the base and 4 to 12 staminate (male) flowers above; [3] alternatively, all flowers may be of the same sex. Male and female flowers have five petals and five sepals, all of which are scaly on the outer surface. Five orange glands are located immediately inside the sepals. Male flowers have yellowish petals and 14 to 18 stamens. Female flowers have three down-curved style branches above a squat, scaly ovary. [5] The plant is pollinated by insects such as beetles [3] and bees. [9] Flowering occurs mostly from late February until early April. [2]
The fruit is a light brown [5] 3–celled [3] capsule 0.6 to 0.8 cm in length [5] that is borne on a pedicel. Seeds are 6.7 to 7.9 mm long and 5.2 to 6.0 mm wide. They are dark brown to nearly black with white blotches and streaks and have a yellow caruncle below a prominent white keel at the point of attachment. Seeds are explosively dehisced from the capsule. [3] Fruiting occurs between May and June. [2]
Texabama croton is restricted to the eastern Edwards Plateau [3] and southern Cross Timbers [10] within Travis, Bell and Coryell counties. Within this limited range, it has a very patchy distribution and is abundant in the few niches where it occurs and is absent elsewhere. In addition, it is separated from populations of the nominate variety of C. alabamensis by more than 1000 km. [3] C. alabamensis var. texensis inhabits pockets of deep soils within forested, mesic canyons and upland oak mottes [4] at elevations of 200 to 400 m. [2]
Plants inhabit mesic canyons within Balcones Canyonlands National Wildlife Refuge [4] and Fort Cavazos's Owl Creek Mountains, [10] where it is typically an understory species forming colonies in the shade of trees such as Texas red oak ( Quercus buckleyi ), chinkapin oak (Q. muehlenbergii), Texas ash ( Fraxinus texensis ), Arizona walnut ( Juglans major ), and escarpment black cherry ( Prunus serotina var. eximia ). [4] It generally grows in moderately alkaline stony clays or clay loams above Cretaceous limestone. [3] Plants growing in full shade are typically longer lived, flower less frequently, and occur at higher densities than those growing in partial shade. [3] Isolated plants occasionally occur in sunny forest margins, [4] where they are stunted and do not flower prolifically. Although bigtooth maple ( Acer grandidentatum ) and Texabama croton have very similar habitat preferences, they are typically not found growing together. It is believed this is due to competition between the species, with the croton succeeding in canyons that are drier and/or more wildfire-prone and the maple succeeding in more mesic habitat. [3]
Plants prefer upland mottes near Lake Travis, where it grows below Texas live oak ( Quercus fusiformis ) within deep, friable soils. [4]
Beetles have been observed feeding on the pollen of Croton alabamensis var. texensis. [3] Goatweed butterfly ( Anaea andria ) caterpillars feed on the leaves of the plant. The flowers are visited by adult butterflies of many species, such as the great purple hairstreak (Atlides halesus). [11]
Molecular clock analysis suggests Croton alabamensis var. texensis diverged from the nominate variety of C. alabamensis in the Quaternary. Allopatric speciation has been proposed as a mechanism to explain the divergence of the varieties. In this theory, geographically intermediate populations between the species current range of Texas and Alabama gradually became extirpated. [9]
Croton alabamensis var. texensis is considered an Imperiled variety by NatureServe. [1] It is primarily threatened by suburban development. [9] Texabama croton is one of 27 species of concern protected by the Balcones Canyonlands Conservation Plan. [12] Protected populations of the plant occur within Balcones Canyonlands National Wildlife Refuge, Pace Bend Park, [9] and Fort Cavazos, which has a population of around 20,000 plants. [10] Staff of the Lady Bird Johnson Wildflower Center have collected seeds of the plant for storage at the National Laboratory for Genetic Resources Preservation in Fort Collins, Colorado. [12]
Texabama croton was discovered in April 1989 at Fort Cavazos in Coryell County by Carol Beardmore and Rex Wahl. [12] Two months later, plants were independently discovered by Chuck Sexton approximately 70 km to the south on the Post Oak Ridge [13] of the future Balcones Canyonlands National Wildlife Refuge in northwestern Travis County. [12] [14] Steve Ginzbarg, a botanist at the University of Texas at Austin, formally described it as a distinct variety of C. alabamensis in 1992. [13]
Texabama croton is valued as an ornamental plant for its attractive, spicily aromatic foliage and propensity to form airy thickets when grown in shade. If cultivated in full sun with irrigation, plants will grow into dense shrubs. Plants can be propagated from stratified seed and softwood cuttings. [15] Cultivated specimens exist at the Lady Bird Johnson Wildflower Center. [16]
The Texas Hill Country is a geographic region of Central and South Texas, forming the southeast part of the Edwards Plateau. Given its location, climate, terrain, and vegetation, the Hill Country can be considered the border between the American Southeast and Southwest. The region represents the very remote rural countryside of Central Texas, but also is home to growing suburban neighborhoods and affluent retirement communities.
The Edwards Plateau is a geographic region forming the crossroads of Central, South and West Texas, United States. It is named in honor of Haden Edwards. It is bounded by the Balcones Fault to the south and east; the Llano Uplift and the Llano Estacado to the north; and the Pecos River and Chihuahuan Desert to the west. San Angelo, Austin, San Antonio and Del Rio roughly outline the area. The plateau, especially its southeast portion, is also known as the Texas Hill Country.
Quercus macrocarpa, the bur oak or burr oak, is a species of oak tree native to eastern North America. It is in the white oak section, Quercus sect. Quercus, and is also called mossycup oak, mossycup white oak, blue oak, or scrub oak. The acorns are the largest of any North American oak, and are important food for wildlife.
Eriophyllum lanatum, with the common names common woolly sunflower, Oregon sunshine and golden yarrow, is a common, widespread, North American plant in the family Asteraceae.
The golden-cheeked warbler is an endangered species of bird that breeds in Central Texas, from Palo Pinto County southwestward along the eastern and southern edge of the Edwards Plateau to Kinney County. The golden-cheeked warbler is the only bird species with a breeding range endemic to Texas.
The black-capped vireo is a small bird native to the United States and Mexico. It was listed as an endangered species in the United States in 1987. It is the only Vireo that is sexually dichromatic. Recovery of the species' population contributed to its delisting in 2018. The IUCN lists the species as "near threatened."
Neltuma glandulosa, formerly Prosopis glandulosa, commonly known as honey mesquite, is a species of small to medium-sized, thorny shrub or tree in the legume family (Fabaceae).
Rhododendron calendulaceum, the flame azalea, is a species of Rhododendron. It is a deciduous shrub that grows up to 120–450 cm tall. This species of Rhododendron is native to the Appalachian Mountains in the eastern United States, ranging from southern Pennsylvania and Ohio to northern Georgia. It may be extirpated from Pennsylvania and Alabama. It occurs naturally in mixed deciduous forests and is typically found in woodland slopes and mountain balds in the Appalachians, where it prefers dry and rocky mountain woods. The inflorescences of Rhododendron calendulaceum are visited by many animals such as bees, butterflies, hummingbirds and small mammals. It is a popular cultivated plant due to its bright yellow, orange or red flowers.
Echinocereus reichenbachii is a perennial plant and shrub in the cactus family. The species is native to the Chihuahuan Desert and parts of northern Mexico and the southern United States, where they grow at elevations up to 1,500 meters (4,900 ft). This cactus earned the Royal Horticultural Society's Award of Garden Merit.
Ericameria nauseosa, commonly known as chamisa, rubber rabbitbrush, and gray rabbitbrush, is a shrub in the sunflower family (Aster) found in the arid regions of western North America.
Croton alabamensis, known as Alabama croton, is a rare species of flowering plant in the spurge family, Euphorbiaceae, that is endemic to Texas and Alabama in the Southeastern United States. It has two varieties whose ranges are separated by more than 1000 km: Croton alabamensis var. alabamensis is found in two central Alabama counties, while Croton alabamensis var. texensis is found in three counties in Texas.
Caltha leptosepala, the white marsh marigold, twinflowered marsh marigold, or broadleaved marsh marigold, is a North American species of flowering plant in the buttercup family. The species has regionally distinct variations.
Eriogonum longifolium var. lindheimeri, commonly known as Lindheimer's long-leaf eriogonum and Lindheimer's buckwheat, is a dicot of the family Polygonaceae, found in New Mexico and Texas.
Rhus copallinum, the winged sumac, shining sumac, dwarf sumac or flameleaf sumac, is a species of flowering plant in the cashew family (Anacardiaceae) that is native to eastern North America. It is a deciduous tree growing to 3.5–5.5 metres (11–18 ft) tall and an equal spread with a rounded crown. A 5-year-old sapling will stand about 2.5 metres (8.2 ft).
Glossopetalon spinescens, syn. Forsellesia spinescens, is a species of flowering shrub in the family Crossosomataceae known by the common names greasebush, spiny greasebush, Nevada greasewood and spring greasebush.
Balcones Canyonlands is a national wildlife refuge located in the Texas Hill Country to the northwest of Lago Vista, Texas. The refuge was formed in 1992 to conserve habitat for two endangered songbirds, the golden-cheeked warbler and the black-capped vireo, and to preserve Texas Hill Country habitat for numerous other wildlife species. The refuge augments a similarly named preserve in Austin called the Balcones Canyonlands Preserve.
The Southeastern mixed forests are an ecoregion of the temperate broadleaf and mixed forest biome, in the lower portion of the Eastern United States.
Mimosa aculeaticarpa is a species of woody shrub in the family Fabaceae. It is commonly known as the catclaw mimosa or the wait-a-minute bush, and is endemic to upland regions of Mexico and the Southwestern United States, particularly Arizona, New Mexico and Texas.
Holodiscus dumosus is a species of flowering plant in the rose family, with the common names mountain spray, rock-spiraea, bush oceanspray, and glandular oceanspray.
The flora of the Colorado Plateau and Canyonlands region is generally characterized by plant adaptations to the arid conditions of the region, and a wide variation of plant communities from wide variations in elevation and soil types. The elevation variation results in temperature variation. Differing soil types are largely due to erosion of different sedimentary layers in the canyons, from the layers at lowest point of canyons of the Colorado River network, to the top layers of the plateau. Exceptions to flora adapted to aridity occur in lowland riparian areas, at springs, and in hanging gardens.
