Synonyms

The following names are used for this species in botanical and viticultural literature: Vitis rupestris Scheele, Vitis populi foliis Lindheimer, as well as American folk names — Sand grape, Sugar grape, Mountain grape, and Rock grape according to T. Munson's classification.

History of Study and Introduction

Since the precise identification and description of this species made by the German botanist A. Scheele in 1848 (journal Linnaea, t. XXI, p. 591), its scientific name has remained unchanged due to the exceptionally clear and stable features of its pure forms. The only exception is a herbarium specimen collected by F. Lindheimer between San Antonio and New Braunfels, preserved under the name Vitis populi foliis. The name "Mountain grape" was recorded by C. Wright in 1851 on a specimen from New Mexico.
The species was present in European ampelographic collections for a long time, but mass imports for practical viticulture began in the 1880s. Thanks to extensive research and vine collections conducted by Hermann Jaeger in Arkansas, the Indian Territory, southwest Missouri, and northern Texas, around 1885, various forms of this species were introduced into European vineyards to combat phylloxera.

Distribution and Ecological Conditions

Wild populations of Vitis rupestris are strictly limited to specific natural conditions. The vine is never found on the rich, deep black soils of the American prairies, where it is completely displaced by herbaceous vegetation; its range is confined exclusively to the rocky beds of drying forest streams, torrents, and canyons.
The soil profile in its habitats consists of a thick, heavy layer of rocky-gravelly scree. The powerful root system of the vine is capable of penetrating to a great depth through these rocky fractions, which allows the plant to provide itself with moisture and remain completely protected from severe summer drought. In the midst of summer, when the sun completely burns the surrounding vegetation, the leaves of this grapevine remain bright green. A characteristic natural feature of the species, which is preserved during cultivation, is the early natural bareness of the base of the shoots (shedding of the lower leaves).
The species demonstrates colossal frost resistance: in southwest Missouri, wild vines withstand a winter drop in temperature to -28 °C without any damage. When growing on open ground without supports, the shoots trail along the rocky bottom, and their tendrils atrophy as unnecessary; however, upon meeting any shrub or rock ledge, the tendrils instantly develop, firmly securing the vine to the support.

Morphological Variability and Classification of Forms

Despite the stability of its key features, Vitis rupestris includes a huge number of local forms (H. Jaeger isolated and described more than 100 wild types differing in vigor, leaf shape, and productivity). All wild forms are divided into two fundamental morphological groups:

  • Small-leaved group: Characterized by a pronounced bushy, compact habit of the bush with an abundance of vertically directed secondary and tertiary shoots with relatively short main vines. The leaves are small, dense, intensely folded along the central vein (like the pages of a closing book) and arranged on the shoot so densely that they seem to overlap each other (imbricate). The teeth are simple, single-rowed, relatively deep, and sharp. The group is divided into two subgroups:
    — Types with shiny leaves: The leaf blade is intensely shiny on both sides, young herbaceous shoots have a pronounced wine-red color. They possess a very thick trunk, huge vigor, and inhabit the driest, scorched rocky areas.
    — Types with matte leaves: The upper side of the blade is matte, the underside is of a pale yellowish-green tint. The shoots are green, without shine. They possess reduced vigor, are highly susceptible to lime chlorosis and premature leaf fall.
  • Large-leaved group: Forms powerful bushes with a thick trunk without a pronounced bushy density; lateral branching is much weaker developed. The leaves are large, folded in the shape of a wide trough, more open and loose. It includes three main subgroups:
    — Types with thick wrinkled leaves: The leaf blade is fleshy, slightly folded, the teeth are two-rowed, obtuse. The petioles and young shoots are colored pink, the veins on the underside have a wine-red tint.
    — Types with smooth shiny leaves: The leaves are very juicy, shiny, intensely bent backward along the edges. The veins are light, the shoots are green (colored wine-red only in the region of the nodes). The most trailing, creeping forms belong to this subgroup.
    — Types with flat thin leaves: The leaves reach extreme sizes for the species (up to 14×12 cm), the upper side is matte, the underside has a golden sheen. The teeth are two-rowed, sharp, ending in a long point. The veins are light, the matured wood has a dirty-red tint. Presumably, these forms carry traces of ancient natural hybridization with other species.

Anatomical and Morphological Description of Organs

  • Bush: Possesses a bushy or creeping growth habit with a strictly vertical direction of numerous secondary shoots (laterals). The trunk develops rapidly, becoming very thick. The bark is dense, deeply furrowed, separating in long, narrow longitudinal strips. The wood is durable, with a narrow pith. The root system is powerful, deeply penetrating, of a taproot type with an abundance of branched fine roots.
  • Shoots: Long, smooth, circular in cross-section, straight, rigid. Internodes are short or very short (averaging from 5 to 6 cm). In the herbaceous state, the shoots are completely hairless, smooth, intensely shiny, of a dark green or bright wine-red color depending on the form. The matured vine acquires a characteristic hazel-brown, chestnut, or matte dark gray color. Nodes are weakly expressed, flattened. Tendrils are intermittent, thin, short, and rudimentary during creeping growth on the ground; upon contact with a support, they develop into strong, forked or bifurcated structures of a green or purple color.
  • Leaves: Small (rarely medium), wider than long, symmetrical, round-reniform or broadly ovate in shape. The leaf blade is intensely folded in the form of a trough along the central vein, rigid, dense, leathery. The upper and lower sides of the leaf blade are absolutely hairless, smooth, and shiny. The petiole sinus is completely absent (zero), the margins of the sinus are widely separated, forming a straight or slightly convex line; five main veins converge at the base of the petiole on a small raised "monticule" and seem to be its direct continuation. The teeth are large, wide at the base, triangular, single-rowed or two-rowed, very sharp, ending in a rigid point. The autumn color of the leaves is a clean, lemon-yellow. The petiole is short, strong, hairless, often colored wine-red.
  • Fruit and Clusters: The cluster is small, loose, of cylindrical or indefinite shape, often branched, with small wings. The peduncle is long, thin, green or pinkish. Pedicels are short, thick, with a barely noticeable ring and small warts; when harvested, the berry separates with difficulty, leaving a short brush-like strand intensely colored in red. The berries are small, rounded, black with a deep purple tint, with a faint pruinose bloom. The skin is thin, delicate. The pulp is juicy, melting, the juice is intensely colored in dark red, almost black. The taste is clean, neutral, without specific varietal flavors, with high sugar content and pleasant acidity.
  • Seeds: Small, round-spherical, swollen. The beak is very short, thick, weakly separated from the body of the seed. The chalaza is elongated, oval, flat, weakly projecting above the surface. The seed seam is rudimentary, weakly expressed, almost completely merging with the chalaza. On the ventral side, there are two narrow and deep depressions. The surface of the seed is smooth, matte, chestnut-brown.

Resistance to Diseases and Pests

The species Vitis rupestris possesses the highest resistance to the root form of phylloxera, thanks to which it became a key element in the restoration of global vineyards. With insect punctures on young roots, small nodules (nodosities) are formed, which are quickly isolated by cork tissue and do not lead to root death; deep damage (tuberosities) on old roots is not recorded.
The leaves of the species possess absolute immunity to the leaf form of phylloxera (galls are never formed), and also demonstrate the highest resistance to downy mildew (mildew), powdery mildew (oidium), and black rot. The main biological disadvantage of the root system is its high sensitivity to root rot (honey fungus) in conditions of excessive soil moisture and poor aeration, as well as complete intolerance to lime — on carbonaceous soils with an active lime content of more than 10%, the vine instantly falls ill with severe lime chlorosis.

Main Cultural Varieties

In commercial viticulture, two selected purebred forms of the species received the greatest distribution:

  • Rupestris du Lot: Also known under the synonyms Rupestris Phenomenon and Rupestris St. George. It is a sterile male clone, accidentally imported from the USA and isolated in the Lot department. It possesses colossal vigor and a very thick trunk, the diameter of which after grafting often exceeds the diameter of the scion. This is the only exception among pure forms of the species capable of withstanding up to 20–30% of dry chalk in the soil without signs of chlorosis. Shoots root satisfactorily (the average yield in nurseries is 40–45%), forming ideal unions without swellings. The disadvantage is excessive vigor on fertile soils, causing flower shedding (coulure) in grafted varieties.
  • Rupestris Martin: Isolated by the breeder J. Couderc. It is a benchmark representative of the species in terms of adaptive properties. It forms a powerful bush with long, sinuous, sparsely branched shoots of a dark chestnut color. It possesses absolute phylloxera resistance and an unsurpassed ability to develop on the poorest, driest, stoniest, and most barren screes, where other rootstocks perish from drought. However, it absolutely does not tolerate carbonaceous and wet soils. The rooting capacity of shoots and affinity during bench grafting are somewhat lower than in the du Lot variety.