Common Names: Greenbrier, Catbrier, Horsebrier

Class: Liliopsida
Order: Liliales
Family: Liliaceae
Subfamily: Smilaceae (alt. family)
Tribe: undetermined
Genus: Smilax

S. rotundifolia is a high-climbing vine often reaching heights of 10 m. It is a woody, deciduous or partly evergreen vine (Huxley 1992). Stems are wiry, prickly and often 4-angled, and leaves are glossy, ovate to nearly round, and 2-6 inches long (Everett 1982). Leaves are also dark green, entire or finely spinulose with a cordate, truncate or rounded base (Radford 1968). Further, leaves are 5-veined with a thick, leathery texture. Flowers are green-yellow in single umbels. Peduncles are 5-15 mm, flattened, and slightly longer than the petioles (Huxley 1992). Umbels are generally located in the first and second leaf axils but are often found in the third and fourth as well. There may be up to 12 fruit. Pedicels are 5-12 mm in staminate flowers and 3-7mm in pistillate flowers. Likewise, the tepals are 5-6 mm in the staminate and 3-4 mm in the pistillate. Berries have between one and three seeds, are bluish black, and are 5-8 mm in diameter. For another image of S. rotundifolia, click here.

S. rotundifolia was first described by Linnaeaus. The Kewenis Index lists species, who first described them, and the journal where the description can be found. The list, however, is in an abbreviated form, and I was unsuccessful at determining the name of the journal from these abbreviations. The journal is likely to be very old, and pertinent information is probably in Latin. For these reasons, information on where the original specimen was collected and is now deposited are not included. The entry from the Kewensis Index under Smilax is as follows:

rotundifolia, Linn. Sp. Pl. 1030.-Am. bor.

The Manual of the Vascular Flora of the Carolinas (Radford, Ahles, Bell) contains a key that fully describes S. rotundifolia.

GEOGRAPHY

S. rotundifolia is one of the most abundant species of its genus. It can be found throughout the Southeastern United States and is also found in Nova Scotia, Michigan, and Texas. The decline of the species in Canada has been noted and will be discussed further later. It is generally found in woods and moist thickets (Everett 1982).

Smilax rotundifolim L.

NATURAL HISTORY

S. rotundifolia is a well-represented species in most areas that it inhabits. Since the vine sends out long underground stolons from which new shoots arise far from the parent plant, it is often hard to control. It is not unusual for impenetrable thickets to be formed. These vines are, hence, too aggressive to be used in landscaping unless the goal is to cover large banks or deter trespassers. S. rotundifolia can grow in ordinary soil and partial sunshine with little difficulty. Propagation is achieved through seeds or division (Everett 1982).

Evidence of the amazing growth ability of S. rotundifolia can be seen in an Oak forest in Southwestern Virginia. A study was carried out that determined the relative abundance of species in the forest in 1971. Twenty years later, the species abundance was surveyed again. S. rotundifolia which was nearly absent in 1971 had increased 16 fold in the upper stand of the woods and had doubled in the lower stand. The changes noted are the usual successional changes that are expected in an undisturbed community (Rhoades 1992).

The extaordinary growth of S. rotundifolia may be partially attributed to its ability to compete with other species for sunlight. The vines are common in both partial and full sunlight, and thus may possess a broad intraspecific physiological plasticity which strongly affects survival, growth, and competitive ability. The way a vine climbs and the distance it can span between supports determines to a great degree where the vine will grow successfully. It could be that physiological adaptability to lower sunlight is coupled to a climbing mechanism that allows better competition for light. Darwin noted that vines which climb by attaching to stems or bark are more efficient than those which simply twine around their support. He considered the development of tendrils a further improvement since vines employing this mechanism could reach canopy tops while investing little biomass in tendrils. S. rotundifolia climbs using tendrils and, therefore, may have a competitive advantage over other vines that climb by twining.

To spite the success of S. rotundifolia in many areas, there has been a noted decline in its presence in the Carolinian forests in Canada. A study was conducted to determine the breeding system of the vine and its pollination requirements in hopes of understanding is distribution. This could provide a basis for conservation management of the species. The results of the study showed that the flowers are sexually dimorphic. Pistillate flowers have no functional stamens, and staminate flowers lack gynoecial development. Pollen grains produced by staminate flowers are linked to each other by threads of viscin. The grains are 0.3 m in diameter and are tricolporate. Staminate flowers are notably larger than pistillate flowers, and the staminate inflorescences have slightly fewer flowers. No known pollinators could be found. Only three insects visited the pistillate flowers in 50 hours and none visited the staminate flowers. The were between one and four seeds in each fruit . Upon examination of 120 of the fruits, it was found that there was a significant correlation between the size of fruits and the number of smooth seeds present. Conclusions of the study were that S. rotundifolia is an outcrossing species that is apparently dependent on insects for pollination. Candidates for pollinators are mosquitos, small flies, small bees, and bumble bees. It would appear that the fecundity of the plant is most severely limited by the absence of mates. Deficiency of pollinators or the loss of fruit to birds and deer could also contribute (Kevan 1991).

HOW TO ENCOUNTER

As you already know, Smilax rotundifolia is extremely common in the Southeast. It can be observed readily at Sam's Farm. No coordinates are necessary for a plot at the farm since the vine can be readily spotted at many locations in the second growth forest as well as in the old field. The identification guide on this page will be helpful in determining which species of Smilax you are viewing. There are several species present on the farm, but S. rotundifolia is fairly abundant. There is nothing poisonous about the vine, so when you spot it, you can pick it. It may be on the floor of the forest or ascending trees there. If you pull a vine but are not sure that it is this species, specimens at the UGA herbarium can help you determine what it is.

REFERENCES

Carter, Gregory A. & Alan H. Teramura. 1988. Vine Photosynthesis and Relationships to Climbing Mechanics in a Forest Understory. American Journal of Botany. 75(7): 1011-1018.

Everett, Thomas H. 1982. The New York Botanical Garden Illustrated Encyclopedia of Horticulture. Garland Publishing, Inc. New York. Vol. 9 pp 3165-3166

Huxley, Anthony. 1992. The New Royal Horticultural Society Dictionary of Gardening. Macmillan Press Limited. London. v.4. pp 304-305

Jackson, B. Daydon & Joseph Hooker. 1895. Index Kewensis. Clarendon Press. Oxford. pp 925-927

Jones, Samuel B. & Nancy Craft Coile. 1988. The Distribution of the Vascular Flora of Georgia. Athens, GA. pp63

Kevan, Peter G., John D. Ambrose & James R. Kemp.1991. Pollination in an understorey vine, Smilax rotundifolia , a threatened plant of the Carolinian forests in Canada. Canadian Journal of Botany. Vol.69: 2555-2558.

Radford, A.E., H.E. Ahles & C.R. Bell. 1968. Manual of the Vascular Flora of the Carolinas. University of North Carolina Press. Chapel Hill, NC. pp284-289

Rhoades, Richard W. 1992. Compositional Changes in an Oak Forest in Southwestern Virginia after Twenty Years. Castanea 57(4): 252-263.