History of Study and Origin

The nomenclature and taxonomy of the species Vitis candicans did not cause serious disagreement among researchers. The Latin name proposed by the botanist Engelmann became firmly established in scientific use. The researcher Buckley described this plant under the name Vitis mustangensis, but the botanists Durand and Asa Gray identified this error, as Buckley's work was published later than Engelmann's. Local Native American tribes traditionally called this grapevine the Mustang grape—a metaphor that European colonists subsequently adopted and adapted to designate this wild vine.

The botanist Chapman mistakenly classified the Mustang grape as a mere variety of the species Vitis rotundifolia. After the onset of the phylloxera crisis in Europe, the plant was introduced to France. Despite the exceptional vigor of the vine, the species did not gain traction in commercial viticulture due to the extremely low survival rate of cuttings: this grapevine is recognized as the most resistant to cutting propagation and layering among all representatives of the genus Vitis.

Geographical Distribution

The Mustang grape is one of the most abundant and widespread wild species in the southern United States, occupying a dominant niche in its region similar to that of Vitis riparia in the central and northeastern states. The exact northern boundary of its natural range passes along the bed of the Arkansas River, north of which the species is not found in the wild.

The range of the species covers most of the Indian Territory, southwestern Arkansas, parts of Louisiana, and virtually the entire territory of Texas, with the exception of the western areas of the Llano Estacado plateau and the extreme western border defined by the Pecos River. South of Texas, the species crosses the Rio Grande and extends into Mexico, where it is consistently recorded in the states of Tamaulipas, Nuevo León, and Coahuila. A number of authors also note the presence of the vine in southeastern New Mexico, southern Mississippi, Alabama, and northern Florida. The highest population density is recorded in the Texas counties of Bell, Comal, Bexar, and Travis, as well as along the floodplains of the Trinity, Brazos, Colorado, and Guadalupe rivers.

Ecological Features and Adaptability

In its natural habitats, the Mustang grape demonstrates high adaptability to contrasting soil conditions. It grows both on moist, fresh, alluvial, and sandy river deposits of high fertility, and on extremely poor substrates. The plant develops successfully in the specific conditions of the Texas "black waxy lands," characterized by high plasticity, an intense black hue, and elevated acidity. These low-fertility clay soils range from 2 to 18 feet in thickness and lie directly on strata of Cretaceous limestone.

The root system of the vine is capable of penetrating deep into the fissures of yellow and bluish clays without showing signs of lime-induced chlorosis. On pure chalk and limestone formations devoid of a sufficient layer of dark humus (which usually accumulates only in depressions of the relief and on the slopes of hills), the vigor of the vine drops noticeably, and the linear dimensions of the leaf blades decrease. The species possesses an innate resistance to prolonged drought. It frequently coexists on hilltops and slopes with xerophytic vegetation, including cacti, while its leaves show no signs of wilting even during a permanent deficit of moisture.

Synonyms

  • Vitis candicans Engelmann
  • Vitis mustangensis Buckley
  • Vitis taurina Walt.
  • Mustang Grape
  • Mustang

Morphological Description of the Vine and Shoots

Along with Vitis californica, this species forms the most massive trunks and the largest crown spread among North American wild vines. In virgin forests, the circumference of an old trunk reaches 0.5–0.9 meters, and near the headwaters of the Comal River, specimens with a circumference of up to 1 meter 30 centimeters have been recorded. In dense forest tracts, the vine climbs into the crowns of tall trees, completely intertwining with and suppressing them. Living trees turn into natural supports carrying a continuous, sun-impermeable canopy of shoots and leaves of the Mustang grape; the length of such natural galleries in central Texas reaches several hundred meters. In treeless plains, the vine is capable of completely covering isolated dead trees, forming dense, green masses.

Anatomical and morphological characteristics of the shoots:

  • Wood and bark: the wood is tough, fibrous, and has a yellowish-white hue on the cross-section. Beneath the exfoliating bark, the wood layer is grayish-purple. On one-year-old mature shoots, the bark is thin, loosely adherent, and easily separates from the wood.
  • One-year-old shoots: long, strong, slightly wavy, and cylindrical in shape. The coloration ranges from dark brown to reddish-brown with an indistinct luster. Wide, shallow, slightly blurred longitudinal grooves are visible on the surface. In the herbaceous state, the shoots are green or deep dark purple (slightly glaucous) and covered with a continuous, dense layer of felt-like down.
  • Nodes and internodes: the nodes are large, thickened, and flattened in the plane of leaf attachment. The internodes are of medium length. The buds are small and conical.
  • Internal structure of the shoot: the pith is dense, homogeneous, of a pinkish-white or dark auburn hue, and occupies up to two-thirds of the total diameter of the wood. At the level of the nodes, the pith expands noticeably. The diaphragms are flat, flat on the internode side, or plano-concave, weakly lignified, and reach a thickness of 4 millimeters.
  • Tendrils: the arrangement is discontinuous. The tendrils are very powerful, thick at the base, divided into two or three branches, and during the growing season are covered with dense down and have a dark purple color.

Characteristics of Leaves

The leaves are medium in size: the average length is 12 centimeters, and the width is 11 centimeters. The shape of the leaf blade is entire, distinctly cordate or round-cordate. On sprouts and young shoots, the leaves can be deeply and symmetrically dissected into three or five lobes without clear dominance of the central lobe, but as the vine matures, the dissected leaves are completely replaced by entire ones.

Morphological details of the leaf blade:

  • Blade: very thick, dense, leathery, and brittle when broken. The leaf margins are intensely turned downward, giving the leaf a characteristic convex, bell-like shape. Leaves developing in unfavorable dry conditions are smaller in size, possess a thicker parenchyma (spongy tissue), shortened shoot internodes, and a matte-green coloration on the upper side.
  • Sinuses and teeth: the petiolar sinus is shallow, open, and has the shape of a wide letter V; the anchor-shaped cutout is practically absent. The marginal teeth are wide, flat, and smoothed, forming a weakly discernible crenate margin. The teeth terminate in short, yellowish, stiff points.
  • Pubescence: the upper surface of the leaf is smooth, intensely dark green, glossy, with traces of sparse hairs along the main veins. The lower surface is regularly and extremely densely covered with a compact, cotton-like felted down of a milky-white color.
  • Veins and petiole: the main veins are strong, projecting prominently on the lower side, and are colored pink at their base. The leaf petiole is short, sturdy, polygonal in cross-section, dark purple or wine-colored, and covered with dense down.

Anatomical Features (according to M. Gard)

Microscopic examination of the internal tissues of the leaf reveals the following specific features of the species: the cells of the lower epidermis of the leaf blade have irregular, branched contours. The cells of the spongy parenchyma are also highly deformed, branched, and form very large intercellular spaces. The cork layer of the stem consists of 4–6 rows of small cells with distinct thickenings, with two or three of the outer layers being completely sclerified and bearing a punctate structure.

Description of Fruits and Seeds

Parameters of the fruit clusters, berries, and seeds of the wild Mustang grape:

  • Cluster: small, loose, of an irregular branched shape, consisting of a small number of scattered berries. The cluster peduncle is short, of medium thickness, and widens noticeably at the node of attachment to the shoot. The berry pedicels are short and sturdy.
  • Berries: large or medium, round or slightly flattened at the poles (discoid) in shape. According to Buckley's descriptions, the diameter of individual berries can reach 2.5 centimeters. The color of the skin is pure black, covered with a thin layer of glaucous bloom. The flesh is of a rubbery, dense consistency, and juice is weakly released. The skin is thick, strong, and tough.
  • Taste qualities and juice properties: the juice and flesh possess a distinctly acrid, astringent, and burning taste. Due to the high concentration of organic acids, eating fresh berries causes a persistent, painful burning sensation in the throat. The inner side of the skin contains an intense coloring pigment of a dull pinkish-wine shade. When the berry is detached from the pedicel, the dense flesh is often held on the stalk along with a specific wine-red bundle of vessels. The natural wine produced by the local population from the wild Mustang grape in Texas has a harsh, unpleasant, and coarse taste.
  • Seeds: 2 to 3 seeds are formed in the berry. The seeds are large, massive (length is 7–8 millimeters, width is up to 5 millimeters), and of an asymmetrical, elongated-triangular shape. The dorsal side of the seed is shiny, smooth, and colored dark brown or wine-red. The fossettes are weakly developed, and the chalaza is indistinct. The seed beak is short and blunt (the appearance and proportions of the seeds are shown in fig. 652–653).

Hybridization and Use in Culture

The root system of the Mustang grape possesses high immunity to phylloxera, but in extremely dry and hot regions on sandy soils, this immunity may prove insufficient for complete protection. The species is one of the first to flower and blooms for a very long period, which accounts for the abundance of natural interspecific hybrids in the wild. In northern Texas and southern Indian Territory, populations of the Mustang grape regularly mix with Vitis cordifolia and Vitis cinerea. Wild Candicans × Lincecumii hybrids are found everywhere.

Natural complex hybrids known as "Champins" are also described, including combinations of Candicans × Rupestris, Candicans × Berlandieri, and Candicans × Monticola. There are natural crosses of Riparia × Candicans (which include the varietal groups Solonis, Novo-Mexicana, and Doaniana), as well as a hybrid of Æstivalis × Candicans recorded by the scientist Millardet.

In artificial crossing with cultivated European grapevines (Vitis vinifera), the Mustang grape transmits high vigor, a thickened trunk, and drought resistance to the offspring. Nevertheless, first-generation hybrids are unsuitable as direct producers, since the specific tart and astringent flavor of the wild ancestor strongly dominates in the berries and is transmitted to the wine materials. Furthermore, according to the observations of the scientist Millardet, Candicans × Vinifera hybrids are prone to the formation of phylloxera tuberosities and nodosities on the root ramifications, which reduces their value as rootstock material.