Round-leaved greenbrier (Smilax rotundifolia) COSEWIC assessment and status report: chapter 3
Species Information
Name and classification
Scientific name:
Smilax rotundifolia L.
Pertinent synonyms:
None in recent regular usage, but note: Smilax caduca L.; S. quadrangularis Muhlenberg ex Willdenow
Common name:
Round-leaved greenbrier, roundleaf greenbrier, common greenbrier, common catbrier
Family name:
Smilacaceae, Greenbrier Family (often included within Liliaceae by earlier authors)
Major plant group:
Angiosperm, monocotyledon
Morphological description
Round-leaved greenbrier is a perennial woody vine that climbs over shrubs and into trees, to four metres or more (Figure 1). Branches are rounded in cross-section, and branchlets sometimes four-angled, with stout, flattened prickles on major stems. Leaves are alternate, simple, ovate to broadly ovate with cordate bases and reticulate secondary venation, much as in bristly greenbrier (S.tamnoides (= S. hispida; S. tamnoides var. hispida)). Plants are dioecious; flowers are small and green; inflorescences with peduncles about as long as the subtending petioles. Berries are few, in a compact umbel. Further descriptions can be found in Fernald (1950), Voss (1972), Scoggan (1978-1979), Soper and Heimburger (1982), Roland (1998), and Holmes (2002).
The male and female flowers are morphologically distinct, with only staminate flowers featuring functional stamens, and only pistillate flowers developing fruiting tissues (photos in Kevan et al. 1991). The staminate flowers are slightly larger than the pistillate ones (averaging 6.6 mm in diameter versus approximately 4.6 mm, in the populations sampled by Kevan et al. 1991), and pistillate inflorescences appear to tend towards slightly higher flower numbers, but the difference was not significant.
There are only two woody monocotyledons in southern Ontario: Round-leaved greenbrier and bristly greenbrier. In most cases these two are easily distinguished by observers familiar with the species, but some sterile specimens of either species can be superficially similar. In particular, large robust climbing bristly greenbrier individuals can closely resemble spineless round-leaved greenbrier until one notices the distinctive dense thin prickles at the very base of bristly greenbrier stems. Key characters differentiating these taxa are presented in Table 1. Round-leaved greenbrier is the only Smilax in Nova Scotia.
Plant parts | Bristly Greenbrier | Round-leaved Greenbrier |
---|---|---|
Prickles | Slender, rounded (spines) and dense (towards base of plant; prickles may be absent from the middle and upper stems). | Broad and flattened at base, typically green with a dark tip and present on most sections of the branches (often less frequent in the upper portions of the plant). |
Fruiting peduncles | At least twice as long as the subtending petiole. | Less than twice as long as the subtending petiole. |
Ripe fruit | Dark, no waxy bloom | Whitish waxy bloom |
Berries | Numerous (10-25) | Few (5-12) |
Cross-section of young branchlets | Round or weakly angled | Four-angled |
Lower leaf surface near petiole | Smooth | Frequently with minute spines |
Rhizomes | Knotted and short | Linear |
This species is well illustrated in Soper and Heimburger (1982), but Gleason's (1963) illustrations of this species and Smilax hispida (=S. tamnoides) are ambiguous.
Genetic description
No genetic investigations are known to have been undertaken on this species, let alone within its Ontario or Nova Scotia ranges. However, the dominant presence of isolated unisexual clones (see Table 2) in the Ontario populations suggests that most of these populations are a) the result of a single dispersal event or at least a very small number of such events and b) not experiencing any gene flow from other populations. As such, individual populations are likely strongly genetically homogeneous. This hypothesized pattern of rare dispersal events (rather than the current populations being remnants of a formerly much more widespread distribution) is supported by the fact that only a single population is known to be extirpated (see Table 2).
Designatable units
Round-leaved greenbrier occurs in two widely separated areas of Canada: southwestern Ontario and the coastal plain in southwestern Nova Scotia. These two areas of distribution warrant separate Designatable Unit designations due to their occurrence in two different Ecological Areas recognized by COSEWIC (Great Lakes Plains and Atlantic) and because of their different conservation status. In Ontario, the Great Lakes Plain population is listed as Threatened provincially and by COSEWIC (2001) in an update report that includes an addendum. The Atlantic population in Nova Scotia is recognized provincially as secure based on the General Status of Species in Canada assessment (Wild Species 2005).
Although the present report includes data on both Designatable Units, the Ontario Unit is covered in greater detail, due to its documented risk of extirpation in the original report (Ambrose 1994). The limited information compiled for the Nova Scotia populations reflects the fact that the species has not been tracked provincially or by the Atlantic Canada Conservation Data Centre because of its relatively high frequency of occurrence and apparently secure status (S4) in the province (NatureServe 2006).
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