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Published In: Species Plantarum 2: 1043. 1753. (1 May 1753) (Sp. Pl.) Name publication detailView in BotanicusView in Biodiversity Heritage Library

Project Name Data (Last Modified On 9/22/2017)
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1. Celtis L. (hackberry)

Plants trees or shrubs to 35 m tall. Bark smooth or with irregular corky warts and/or ridges, pale gray or almost white. Twigs sometimes slightly zigzag, the winter buds axillary, usually with several overlapping scales (naked elsewhere). Leaves spirally alternate in several planes, not 2-ranked. Leaf blades lanceolate, ovate, or triangular, slightly to strongly asymmetric at the base, widest 1/5–1/3 from the base, the secondary veins turning aside and anastomosing before reaching the entire or toothed margins, the basal pair longer and more prominent than the others, thus the blade appearing more or less palmately 3-veined from the base. Flowers staminate and apparently perfect, appearing before the leaves, the staminate flowers in small, dense clusters at the base of current-year’s growth, the perfect flowers solitary in the axils of the lowest expanding leaves of the current season. Calyces 2–3 mm long, shallowly to deeply 4(5)-lobed, but the lobes usually shed early, green to greenish yellow, turning brown after flowering. Stamens with the anthers yellow to greenish yellow. Fruits drupes, the outer layer thin, glabrous, smooth, sometimes somewhat glaucous; the middle layer thin, fleshy, sweet-tasting, the seeds covered by a large, stony endocarp. About 70 species, worldwide.

The genus Celtis is taxonomically very difficult. All characters are variable and identifications are best made using several characters in combination. In the past, this variability was often explained by postulating high levels of hybridization between species. Recent studies have shown that this is false. It is difficult to cross the species in the garden (Whittemore and Townsend, 2007) and hybrids among sexually reproducing taxa are rare or absent in nature (Whittemore, 2005). Instead, C. pumila is apomictic, the seeds developing without pollination, and as in many apomicts there is a great deal of variation from population to population. Interestingly, it is possible to obtain hybrids by placing pollen from sexual species on stigmas of apomictic plants (A. Whittemore, unpublished), and some puzzling forms found in the wild may have originated by pollination of apomictic C. pumila by pollen from C. laevigata or C. occidentalis.

The bark of native Celtis species is characterized by the formation of distinctive corky warts and/or ridges. The species differ in the amount and distribution of corky outgrowths, but the degree of cork development varies from tree to tree and varies with the age of the tree, so this character is not always reliable for species identification. Cork also forms in response to injury, so trunks that have been damaged may form corky outgrowths in unusual places.

Leaves from different parts of the plant or at different stages in its life may be very different in form. In particular, leaves from vigorous leading shoots are much larger than leaves from lateral branches and may differ strikingly in shape and marginal toothing. The shape, texture, and toothing of juvenile leaves may be very different from leaves of adult plants. Unless otherwise stated, descriptions apply to a leaf that is subtending a flower or fruit. Vegetative plants or vegetative, leafy twigs in the herbarium are not always identifiable.

The fruit of hackberries is eaten by many species of mammals and birds. The flesh of the fruit is sweet, with a pleasant flavor, but the stone is large and there is relatively little flesh in the drupe. Some scholars have suggested that the nettle tree of Europe and the Near East, C. australis L., was the lotus of Homer’s Odyssey, the fruit eaten by the Lotus-Eaters of North Africa. Others have felt that Homer’s lotus was more likely a species of Ziziphus Mill. (Rhamnaceae). Fruit of our native Celtis often remain on the tree long into the winter, and sometimes a few fruits even remain on the tree until the following spring.

Hackberry wood is soft and it is not widely used. It is sometimes used for furniture and handcrafts, where its light color is valued.

Some species, especially C. occidentalis, are used in horticulture, as they are fast-growing trees with great tolerance to heat, cold, drought, periodic flooding, rapid changes in temperature and moisture, and poor soils. They are widely grown in dry areas with extreme temperature fluctuations (especially the western Great Plains and the intermountain western states), but their use in Missouri is limited by their susceptibility to several pathogens (Elias, 1970), especially witch’s brooms (caused by mites [Eriophyes sp.] and powdery mildew [Sphaerotheca phytoptophila Kellerm. & Swingle]) and leaf galls (caused by hemipteran insects, Pachypsylla spp.). These pathogens do not harm the plant, but they cause cosmetic damage and reduce its popularity as a shade tree. Hackberries also tend to become weedy in garden settings.

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