Scientific name: Vitis sp.
Origin: Grapes belong to the genus Vitis in the family Vitaceae. The genus is distributed in Europe (1 species)1, Asia (~40 species) and North America (~20 species). While there are perhaps 11 genera and 600 species in the family, Vitis is sometimes claimed to be the only genus that supplies human food.
Grapes present me with a biological conundrum. I consider it almost impossible and unthinkable that a genus would show up in three widely separated locations completely independently. Yet today there are three epicenters for grapes; Europe, Asia and North America. It is the North American grapes that puzzle me. In the taxonomic treatises of North American plants this group of grapes is considered native to this part of the world.2 Originally I considered that a progenitor to today’s North American grapes rode over on North America to its current location after its breakaway from the supercontinent Pangaea, but that would seem to be long before the advent of modern flowers. While I suppose that grapes could have moved from North America to Europe and Asia, it seems more likely that the trip would have been the reverse of that. Because of the food value of the grape it now seems likely to me that members of the genus came from Eurasia or Asia across the Bering Straits perhaps carried by man or some other animal. No matter what the case, the American grape industry seems to be dealing with two major groups of plants, those recently imported from Europe and those that are thought of as North American grapes.
What had become distant cousins, the European grape and the North American grapes, were reunited by the white man, probably in the 17th century, largely to bolster the American wine industry, which was producing a wine from American grapes that was considered quite inferior to the European wines. The European grapes were not resistant to some of the diseases and the insect grape phylloxera (Daktulosphaira vitifòliae) they found in the North America. They also suffered from a lack of cold hardiness. Considerable effort has been directed toward creating solutions to these problems. Arguably, today grapes have quite possibly become the most important fruit crop grown in the world. They provide fresh fruit (table grapes), dried fruit (raisins), fresh grape juice, concentrated grape juice, wine, distilled liquors, grape seed oils, anthocyanin pigments and ethanol production.
Perhaps the most important North American species include V. labrusca, V. aestivalis, V. riparia, and V. berlandieri. Some of their notable characteristics include cold hardiness and disease resistance, and compared to the European grapes, the fruits have lower sugar and higher acid content and are slip-skin.3 The characteristics of the European species, in contrast, include: cold susceptibility, need of a longer growing season with dry summers relatively free of rain, a low relative humidity and susceptibility to North American diseases and pests.
For a variety of reasons, probably mainly to improve the production of wine from the North American species, the European Vitis vinifera has been extensively hybridized with the North American species. The hybrids have been selected for tolerance to many of the fungal diseases of North America, for tolerance to Phylloxera4, cold hardiness and good productions.
Plant description: The genus Vitis in moist climates generally consists of tendril-climbing, woody deciduous vines, whereas in dry climates its members may be almost erect shrubs. The plants have brown pith and usually a shredding bark. The tendrils are simple or branched and often coiled, and slender tipped. The 3 to 6 inch leaves are simple (not compound) and more-or-less palmately lobed.
The flowers are distributed in relatively narrow, loosely branched panicles5 that range between 1 to 10 inches in length and can contain up to several hundred inconspicuous greenish florets about 0.25 in long. Each floret has 2-7 (usually 5) stamens and 5 greenish petals that are united at their apex (compare Figures 1and 2). In the plants used here for photographs the area of this upper attachment was initially somewhat reddish.
The petals of grape flowers are lost in an unusual manner. (see Fig. 1). Initially the petals are attached to the receptacle of the flower, but are also connected together on their upper edge thus making a hood over the sexual parts of the flower. Initially the connection of the petals to the receptacle is lost but the upper connection of the petals to each other remains intact thus forming a ‘cap’ over the flower. Usually after several hours the cap is lost. Flowers with and without caps can be seen in fig. 3. The time period over which this happens is relatively short. The caps seen in the accompanying photo were taken under a low wind condition when there was still enough light for photography. They generally were gone the next morning when again the light was suitable for photography.
The genetic setup
As I began to review the pollination requirements of grapes, I found what appeared to me to be some discrepancies in the literature concerning pollination. To get a better understanding of …