Vitis -- One Genus or Two?
Pierre Galet, in A Practical Ampelography: Grapevine Identification (1979), sowed a seed for thought. In "Appendix 1" (The Genus Vitis) of his work, he noted the general characteristics of the genus and then divided it into two sections, the Vitis Section and the Muscadinia Section. This jarred my memory sufficiently to recall that Thomas V. Munson, in 1909, had divided vitis into two "sections" -- the true grapes (Euvitis) and pseudo grapes (Lenticellosis). Munson placed two species in the latter -- (Vitis Rotundifolia and Vitis Munsoniana -- but Galet added a third -- Vitis Popenoi. This division is more than just interesting.
Both Galet and Munson based the division on such basic differring characters as forked (Vitis) versus unforked (Muscadinia) tendrils, pyriform (Vitis) versus navicular (Muscadinia) seeds, the presence (Vitis) or absence (Muscadinia) of a diaphragm interrupting the pith at the node, and so on. There are, in all, 13 such morphological, anatomical and cytological differences noted, but it is the first listed by Galet (but unknown to Munson in 1909) that speaks the loudest to me -- (Vitis) has n=19 basic chromosomes, while (Muscadinia) has n=20. Further, crosses between the Vitis species will produce viable and fertile descendents, just as crosses between the Muscadinia species will also produce viable and fertile descendants, but crosses of species between the two sections fail. This is not a trivial matter. Galet's suggestion that Muscadinia could, in fact, constitute a new genus of Ampelopsis is quite compelling. However, until there is wide agreement on this (and there isn't), I shall continue as my predecessors in classifying all grapes as genus Vitis. Still, the differing characters between (Vitis) and (Muscadinia) are useful in identification by exclusion of North American natives in the southeastern United States and Mexico.
Characteristics of the Vitis Section
The number of basic chromosomes is n=19 or 2n=38.
The canes have an inner corky layer, outside of which is the bark (including the pericyclic fiber, the primary and part of the secondary phloem) which may shed in strips at maturity.
The secondary phloem has alternating tangential layers of hard and soft phloem.
The secondary wood is soft with large vessels.
There is a substantial amount of pith.
A section of the shoot or cane is always elliptical and never quadrangular. There is a diaphragm which interrupts the pith at the node.
The tendrils are opposite the leaves, two- or three-forked.
There are woolly, bristly or special hair types on the vegetative organs.
The clusters have numerous berries that adhere to the stem until maturity or beyond.
The berries have a sugary and acid juice suitable for eating fresh or making juice or wine.
The seeds are pyriform.
The leaves are generally palmate with five principal veins.
All the species of this section are graftable on each other, but grafting with species from Muscadinia has been found unfeasible. The species in this section will root from cuttings.
Characteristics of the Muscadinia Section
The number of basic chromosomes is n=20 or 2n=40.
The canes have prominent lenticels because of the corky layer just beneath the epiderm. Only the epiderm -- not the bark -- falls off at maturity.
The phloem fibers of the secondary phloem are radically placed, like two uneven columns, underneath the pericycle.
The wood is hard, without large vessels.
There is little pith.
There is no diaphragm interrupting the pith at the node, so the pith is continuous from one end of the cane to the other.
The tendrils are opposite the leaves, always simple and intermittent.
The vegetation is always glabrous or nearly glabrous.
The clusters have relatively few berries that ripen unevenly and drop off one by one at maturity.
The berries are pulpy, with little juice, but generally have low concentrations of sugar and are less suited for vinification.
The seeds are navicular with an oval chalaza surrounded by radiating ridges and furrows.
The leaves are always palmate and nearly entire without lobing.
Grafting between species of this section has not been tried because there is no practical interest in it. Grafting with species from Vitis has not been successful. The species in this section will not root from cuttings, but do root by layering.
For the home winemaker, these differences have modest to severe potential consequences. It certainly is worth knowing that three species, in general, are less suited for winemaking that all the others. At the same time, I would submit that there are more than a few suitable wine grape among the Rotundifolia, so this is not a hard and fast rule. If you collect wild grapes for wine as I do, it is also worth knowing that the Muscadinia tend to drop their fruit as they mature. Finally, when using native plants as rootstock for grafts, it is essential to know that the Muscadinia will not accept grafts from Vitis cuttings, nor will they root as cuttings. These, indeed, are important data.
Last update was November 3rd, 2000.
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