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).

Figure 1.  Terminal portions of round-leaved greenbrier female vines with flowers and fruit (see Holmes 2002, p. 475).

Figure 1.  Terminal portions of round-leaved greenbrier female vines with flowers and fruit (see Holmes 2002, p. 475).

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.

Table 1.  Key characters distinguishing round-leaved greenbrier (Smilax rotundifolia) from bristly greenbrier (Smilax hispida = S. tamnoides; from Holmes 2002; Soper and Heimburger 1982; and Voss 1972).
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).

Table 2. Reproductive status, population size, and trends at Ontarioround-leaved greenbrier sites.
Site # Reproductive status 1994Footnotea Population size 1994Footnotea Reproductive status 2006 Population size 2006
1 Unknown (not fruiting) 2 subpopulations; 20-30 clusters Plants not found.
2 Unisexual: male 3 subpopulations; 12-16 clusters Unable to access.
3 Both male and female: fruiting 3 subpopulations; ~50 clusters Access denied.
4 Unisexual: male 3 subpopulations; ~60 clusters Access denied.
5 Both male and female: fruiting 1 subpop; 7 clusters Not fruiting. Locally abundant (dozens of clusters) and widespread as small clusters (at least two subpopulations, for each of the woodlots)
6 Unisexual: unknown (not fruiting) 1 subpop; 12 clusters Not fruiting. Three main areas; ~6 subpopulations; >100 clusters. Two of the subpopulations each contain dozens of clusters in a more-or-less continuous tangle. Certainly other smaller subpopulations exist in the area, and in several areas for which permission to access was not available.
7 Both male and female: fruiting 1 subpop; 24 clusters One cluster was fruiting. Three subpopulations seen, in close proximity. The larger covered an area of approximately 10m in diameter; the others consisted of a single cluster, and a double cluster.
8 Unisexual: female (not fruiting) 1 subpop; 11 clusters No fruits seen Population extended along Garner Road for 15 m, and was wider further in from the road, extending at least 30 m back in places (but permission to enter the property was not available). Locally dense.
9 Unisexual: unknown (not fruiting) 2 subpopulations; ~6 clusters None found, but permission to access the woodlot where the species most likely occurs was not available.
10 Not surveyed Not fruiting. Abundant. Thousands of stems, in areas very dense (dominant), in mixture of tall tree-climbing plants, and smaller scrubby ones. Area of main patch approximately 0.7 ha (mapped).
11 Unisexual male Access to property was not available in 2006. OMNR surveys in 2004 reported at least five patches, one of which was "large and vigorous."
Permission obtained in 2007 by the Niagara Peninsula Conservation Authority (NPCA) and site visited by M. Oldham with NPCA staff including A. Garofalo on 25 May 2007; hundreds of stems, some climbing to 5 m or more in tree limbs, with plants covering a large linear patch about 50-60 m x 5 m; all flowers seen and examined were male; no threats evident
12 Not surveyed Not fruiting Common in patch ~60 m x 7 m (mapped).
13 Not surveyed None visible from the road (2006). In 2005 fieldworkers reported a patch of approximately 36 m by 10 m. Reproductive status of plants was not noted (Brinker pers. comm. 2006)
14 Presumably extirpated Presumably extirpated

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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