Dwarf hackberry (Celtis tenuifolia) COSEWIC assessment and status report: chapter 3

Species Information

Name and Classification

Scientific name:

Celtis tenuifolia Nutt.

Synonym:

Celtis occidentalis L. var. pumila (Pursh) A. Gray

Common name:

dwarf hackberry

Family:

Ulmaceae (Elm Family)

Major plant group:

Dicot flowering plant

Dwarf hackberry, Celtis tenuifolia, is a small tree or shrub. In the north, there is only one other species of Celtis, C. occidentalis, a medium to large tree. Analysis of morphological and molecular data did not suggest the occurrence of hybridization within three species of Celtis in the southern United States (Buck & Bidlack, 1998). However, in the Ontario populations that are sympatric with C. occidentalis, intermediates in a few characteristics (e.g., pedicel length, leaf l:w ratio, tip attenuation and serration distribution), suggest that some exchange may be taking place. The unclear distinction of the species of Celtis has been noted, as well as being taxonomically complex and in need of revision (Flora North America, 1997).

Description

Dwarf hackberry is a scrubby, many-branched shrub or small tree with one to a few trunks; it is commonly up to 5 m high, occasionally up to 10 m, and resembles witch-hazel (Hamamelis virginiana) in form when multi-trunked. Typical of many members of the family, trunks are composed of relays of oblique branches that secondarily become erect (i.e., all axes are sympodially plagiotropic). In vigorously growing individuals without interference or damage to branches (the exception in this species), the result is a silhouette that is similar to the vase form of American elm. Twig arrangement is also typical of the family, being two ranked and alternate (following the same arrangement of leaves the year before); in this species they are typically short and stiff and under some conditions they become divaricately branched or clustered, especially in response to browsing. Leaf bases are only slightly oblique (cf. strongly oblique in C. occidentalis:), with three distinct veins at the base; margins are entire to toothed mostly above the middle (cf. distinctly toothed to the base); blades ovate with a short tapered tip (lanceolate with a broad base and attenuate-falcate tip, 3.7-6.3 cm long cf. 4.2-12.0 cm). The bark is grey and smooth, developing small knobs and/or small fissures with age (cf. developing a thick corky pattern of knobs and ridges, sometimes recurved). Plants monoecious with unisexual flowers that appear with expanding leaves; fruit matures in late summer, globose, orange-brown coloured and smooth, sweet and sugary (cf. subovoid, olive-purple, becoming puckered, tasteless to bitter), pedicels 3-8 mm long (cf. 9-18 mm).

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