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The families of flowering plants

L. Watson and M.J. Dallwitz

Ulmaceae Mirb.

Including Cannabidaceae p.p., Celtidaceae Link, Samaracaceae Dulac

Habit and leaf form. Trees and shrubs. Plants green and photosynthesizing. Leptocaul. Mesophytic. Leaves persistent, or deciduous; alternate; spiral, or distichous; petiolate; non-sheathing; simple. Lamina entire; pinnately veined, or palmately veined (then with three main veins— Celtidoideae); cross-venulate; oblique at the base (often), or rounded at the base. Leaves stipulate. Stipules interpetiolar, or intrapetiolar; free of one another, or concrescent; caducous. Lamina margins entire, or dentate (or lobulate). Vegetative buds scaly. Leaf development not ‘graminaceous’. Domatia occurring in the family (known from 3 genera); manifested as pockets, or hair tufts.

Leaf anatomy. The leaf lamina dorsiventral (usually), or bifacial to centric (in some Celtis species). Mucilaginous epidermis present. Stomata mainly confined to one surface (abaxial); anomocytic. Hairs present; eglandular and glandular (the former mostly uni- or bicellular, often calcified or silicified, sometimes warty, sometimes with cystolith-like bodies attached to their walls; the latter very variable, commonly each with a glandular head of one to several cells and a unicellular or uniseriate stalk of varying length). Cystoliths commonly present (in epidermis and/or mesophyll, as well as the structures associated with hairs), or absent. The mesophyll containing mucilage cells (in several genera), or not containing mucilage cells; containing crystals. The crystals druses (common in mesophyll), or solitary-prismatic (sometimes around vascular bundles). Minor leaf veins without phloem transfer cells (Celtis, Zelkova).

Axial (stem, wood) anatomy. Pith with diaphragms, or without diaphragms. Cork cambium present; initially superficial. Nodes tri-lacunar. Primary vascular tissues in a cylinder, without separate bundles; collateral. Internal phloem absent. Cortical bundles absent. Medullary bundles absent. Secondary thickening developing from a conventional cambial ring.

The wood ring porous to diffuse porous. The vessels in diffuse porous woods medium, or small and medium; variable in arrangement. The vessel end-walls horizontal; scalariform and simple (rarely), or simple. The vessels without vestured pits; with spiral thickening, or without spiral thickening. The axial xylem with fibre tracheids to without fibre tracheids (the fibres typically with small, simple pits, occasionally with very small bordered ones); with libriform fibres; without septate fibres. The fibres without spiral thickening. The parenchyma usually essentially paratracheal. The secondary phloem stratified into hard (fibrous) and soft (parenchymatous) zones (occasionally), or not stratified. ‘Included’ phloem absent. The wood storied, or partially storied (VP). Tyloses present, or absent.

Reproductive type, pollination. Plants hermaphrodite, or monoecious, or polygamomonoecious. Gynoecium of male flowers vestigial. Pollination entomophilous.

Inflorescence, floral, fruit and seed morphology. Flowers solitary, or aggregated in ‘inflorescences’; when aggregated, in cymes, or in fascicles. The ultimate inflorescence units cymose, or racemose. Inflorescences axillary; usually cymose clusters. Flowers small; regular, or somewhat irregular; cyclic. Free hypanthium present (or arguably so, when stamens are inserted on the perianth), or absent. Hypogynous disk absent.

Perianth sepaline; (2–)5(–9); free, or joined; 1 whorled (ostensibly), or 2 whorled (?—theoretically). Calyx if the perianth is so interpreted, (2–)5(–9); 1 whorled, or 2 whorled; polysepalous, or gamosepalous; unequal but not bilabiate, or regular; persistent; imbricate, or valvate (induplicate-valvate in Trema).

Androecium (2–)4–8(–15) (mostly equalling or twice K). Androecial members adnate (to the bottom of the perianth), or free of the perianth; free of one another; 1 whorled, or 2 whorled. Androecium exclusively of fertile stamens. Stamens (2–)4–8(–15); reduced in number relative to the adjacent perianth, or isomerous with the perianth; oppositisepalous; erect in bud (nearly always), or inflexed in bud (sometimes, in Celtis). Anthers dorsifixed; dehiscing via longitudinal slits; extrorse (e.g. Celtis), or introrse; tetrasporangiate. Endothecium developing fibrous thickenings. Microsporogenesis simultaneous. The initial microspore tetrads tetrahedral, or decussate. Anther wall initially with more than one middle layer (2 to 4). Tapetum glandular. Pollen grains aperturate; 2–5(–6) aperturate; colpate (or rupate), or porate; 2-celled (Holoptelea), or 3-celled (Ulmus).

Gynoecium 2(–3) carpelled. Carpels reduced in number relative to the perianth. The pistil 1 celled, or 2 celled. Gynoecium syncarpous; synovarious to eu-syncarpous; superior. Ovary 1 locular (usually, by abortion), or 2 locular. Gynoecium median; stylate, or non-stylate to stylate. Styles 1–2; free to partially joined; apical. Stigmas 1; dry type; papillate; Group II type. Placentation apical. Ovules in the single cavity 1; pendulous; non-arillate; anatropous, or campylotropous (Celtidoideae); bitegmic; tenuinucellate, or crassinucellate. Outer integument contributing to the micropyle, or not contributing to the micropyle. Embryo-sac development Polygonum-type, or Adoxa-type, or Drusa-type. Polar nuclei fusing prior to fertilization. Antipodal cells formed; 3; proliferating (forming up to 10 cells, in Holoptelea), or not proliferating; ephemeral. Synergids pear-shaped. Hypostase present. Endosperm formation nuclear. Embryogeny onagrad, or solanad.

Fruit fleshy, or non-fleshy; indehiscent; a samara, or a nut, or a drupe. Seeds scantily endospermic, or non-endospermic (usually). Cotyledons 2; flat (Ulmoideae), or folded to rolled (Celtidoideae). Embryo achlorophyllous (2/5); straight (Ulmoideae), or curved (Celtidoideae). Micropyle not zigzag.

Seedling. Germination phanerocotylar. Nitrogen-fixing root nodules present (Parasponia), or absent.

Physiology, phytochemistry. C3. C3 physiology recorded directly in Celtis, Ulmus. Sugars transported as oligosaccharides + sucrose (predominantly, in 4 genera, but some myoinositol usually present as well). Not cyanogenic (usually), or cyanogenic (Trema). Cynogenic constituents tyrosine-derived. Alkaloids present, or absent. Arbutin absent. Iridoids not detected. Saponins/sapogenins present, or absent. Proanthocyanidins present; cyanidin, or cyanidin and delphinidin. Flavonols present, or absent (Celtis, Trema); kaempferol and quercetin (Ulmus). Ellagic acid absent (4 species, 3 genera). Aluminium accumulation not found. Sieve-tube plastids P-type, or S-type (then without starch); when P-type, type I (b).

Geography, cytology. Temperate to tropical. Widespread tropical and temperate. X = 10, 11, 14.

Taxonomy. Subclass Dicotyledonae; Crassinucelli. Dahlgren’s Superorder Malviflorae; Urticales. Cronquist’s Subclass Hamamelidae; Urticales. APG III core angiosperms; core eudicot; Superorder Rosanae; fabid. APG IV Order Rosales.

Species 200. Genera 15; Ampelocera, Celtis, Chaetachme, Gironniera, Hemiptelea, Holoptelea, Lozanella, Parasponia, Phyllostylon, Planera, Pteroceltis, Trema, Ulmus, Zelkova.

General remarks. This compilation has not yet (2017) been updated re more recently revised family circumscriptions, involving transference of Celtis, Pteroceltis, Trema, Gironniera and Lozanella from Ulmaceae to Cannab(id)aceae; cf. Sytsma et al. (2002).

Economic uses, etc. Timber (especially for furniture) from Ulmus (elm), Planera (false sandalwood).


Thou art an elm, my husband, I a vine,
Whose weakness, married to thy stronger state,
Makes me with thy strength to communicate
(‘Comedy of Errors’, ii., 2)

Old Elm that murmured in our chimney top
The sweetest anthem autumn ever made
(John Clare c. 1821, ‘To a Fallen Elm’)

The Elm tree’s heavy foliage meets the eye
Propt in dark masses on the evening sky
(John Clare, fragment before 1856 — contrasted with ash, q.v.)

Ellum hateth
Man, and waiteth
(ancient adage - re. the proneness of large, healthy-looking elms to catastrophic structural failure)

Illustrations. • Le Maout and Decaisne: Celtis, Solenostigma (= Celtis). • Le Maout and Decaisne: Ulmus. • Trema guineensis: Thonner. • Ulmus procera (as U. suberosa) and U. glabra (as U. montana): Eng. Bot. 1285 and 1287, 1868. • Ulmus ‘campestris’ (B. Ent.). • Aphananthe philippinensis: Hook. Ic. Pl. 12 (1876). • Celtis timorensis, as C. cinnamomea: Trimen, Ill. Fl. Ceylon (1898).

We advise against extracting comparative information from the descriptions. This is much more easily achieved using the DELTA data files or the interactive key, which allows access to the character list, illustrations, full and partial descriptions, diagnostic descriptions, differences and similarities between taxa, lists of taxa exhibiting or lacking specified attributes, distributions of character states within any set of taxa, geographical distribution, genera included in each family, and classifications (Dahlgren; Dahlgren, Clifford, and Yeo; Cronquist; APG). See also Guidelines for using data taken from Web publications.

Cite this publication as: ‘Watson, L., and Dallwitz, M.J. 1992 onwards. The families of flowering plants: descriptions, illustrations, identification, and information retrieval. Version: 15th April 2018.’.