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The families of flowering plants

L. Watson and M. J. Dallwitz

Juglandaceae A. Rich. ex Kunth

Including Nuculaceae Lam. & DC., Platycaryaceae Nakai, Pterocaryaceae Nak.; excluding Rhoipteleaceae.

Habit and leaf form. Trees (mostly), or shrubs (a few); often resinous. ‘Normal’ plants. Leptocaul. Leaves deciduous; alternate (mostly), or opposite (Alfaroa, Oreomunnia); petiolate, or sessile; non-sheathing; aromatic (with aromatic, resinous, peltate gland scales, and often with other types of glands in addition); compound; (impari-) pinnate, or ternate. Lamina pinnately veined; cross-venulate. Leaves exstipulate. Vegetative buds brown-hairy, scaly, or not scaly (the buds commonly several, superposed). Leaf development not ‘graminaceous’. Domatia occurring in the family (4 genera); manifested as pits, or pockets, or hair tufts.

Leaf anatomy. The leaf lamina dorsiventral (mostly, with one or two palisade layers), or bifacial (tending to bilateral in Engelhardtia). Stomata present; (often of two distinct sizes on the same leaf) mainly confined to one surface (abaxial); anomocytic. Hairs present; eglandular and glandular (with several different types of each represented, the latter including short-stalked capitate forms and glandular peltate scales). Complex hairs usually present; gladular, peltate. The mesophyll containing crystals. The crystals mostly druses. Minor leaf veins without phloem transfer cells (Juglans).

Axial (stem, wood) anatomy. Pith with diaphragms, or without diaphragms. Secretory cavities absent (but often with scattered secretory cells). Cork cambium present; initially superficial. Nodes tri-lacunar, or multilacunar. 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. Primary medullary rays narrow.

The wood diffuse porous, or ring porous to semi-ring porous. The vessels usually medium (or slightly largeer); in various arrangements, but usually mostly solitary. The vessel end-walls simple, or scalariform and simple. The vessels without vestured pits; with spiral thickening, or without spiral thickening. The axial xylem with tracheids, or without tracheids; without vasicentric tracheids; with fibre tracheids, or without fibre tracheids; with libriform fibres; including septate fibres (rarely), or without septate fibres. The fibres without spiral thickening. The parenchyma typically apotracheal, or apotracheal and paratracheal (often with a little paratracheal in addition). ‘Included’ phloem absent. The wood not storied. Tyloses present, or absent.

Reproductive type, pollination. Plants monoecious (usually), or dioecious (occasionally). Gynoecium of male flowers vestigial, or absent. Pollination anemophilous.

Inflorescence, floral, fruit and seed morphology. Flowers aggregated in ‘inflorescences’ (mostly), or solitary (female flowers sometimes solitary); in catkins (mostly, these usually drooping, sometimes erect, sometimes grouped into terminal panicles), or in racemes (female, sometimes), or in spikes (female, sometimes). Inflorescences mostly in the form of catkins, which may themselves be grouped into terminal panicles; the catkins unisexual, or bisexual with proximal staminate and distal pistillate flowers; female flowers rarely solitary, or in spikes or racemes. Flowers bracteate; two bracteolate, or ebracteolate (the bractlets often adnate to the sepals (male) or to the bract (female), in the latter case often forming a cupulate involucre maturing to form a husk around the fruit); flowers individually small (and inconspicuous).

Perianth sepaline, or vestigial, or absent; when present, (1–)4(–5). Calyx when present, (1–)4(–5); more or less adnate with the bracteoles or obsolete in male flowers, consisting of four calyx teeth or suppressed in female flowers.

Androecium in male flowers, (3–)5–50(–100) (or more — decreasing in number acropetally in the catkin). Androecial members free of the perianth; free of one another. Androecium in male flowers, exclusively of fertile stamens. Stamens (3–)5–50(–100) (or more); diplostemonous to polystemonous; shortly filantherous. Anthers basifixed; dehiscing via longitudinal slits; tetrasporangiate. Anther epidermis persistent. Microsporogenesis simultaneous. The initial microspore tetrads tetrahedral, or isobilateral. Anther wall initially with more than one middle layer. Tapetum glandular. Pollen shed as single grains. Pollen grains aperturate; 3–9(–16) aperturate; porate (3–7), or foraminate to rugate (6–16, Juglans); 2-celled.

Gynoecium 2(–3) carpelled. The pistil 1–8 celled. Gynoecium syncarpous; synovarious to synstylovarious; inferior. Ovary 1 locular (above), or 2(–3) locular (below, usually, but the partitioning falling short of the apex, and sometimes 4–8 celled below, by ‘false’ partitions). Locules secondarily divided by ‘false septa’, or without ‘false septa’. Gynoecium median, or transverse. Epigynous disk absent. Gynoecium shortly stylate, or non-stylate. Styles 1–2; free to partially joined; apical. Stigmas 2; dry type; non-papillate; Group II type. Placentation basal (the ovule borne on top of the partition). Ovules in the single cavity 1; ascending; non-arillate; orthotropous; unitegmic; crassinucellate. Embryo-sac development Polygonum-type. Antipodal cells formed; 3; not proliferating; ephemeral. Endosperm formation nuclear. Embryogeny asterad.

Fruit fleshy, or non-fleshy; indehiscent; a drupe (the softer husk sometimes splitting to release the bony pericarp), or a nut, or a samara. The drupes with one stone. Fruit 1 seeded. Seeds non-endospermic. Embryo well differentiated (large, oily). Cotyledons 2 (often massive, deeply lobed from the false septa, and sculptured). Embryo achlorophyllous (2/4).

Seedling. Germination phanerocotylar, or cryptocotylar.

Physiology, phytochemistry. C3. C3 physiology recorded directly in Juglans. Sugars transported as sugar alcohols + oligosaccharides + sucrose (from 9 species and three genera). Cyanogenic, or not cyanogenic. Alkaloids absent (10 species). Arbutin absent. Iridoids not detected. Proanthocyanidins present, or absent; delphinidin, or cyanidin and delphinidin. Flavonols present, or absent (Pterocarya); quercetin and myricetin (Juglans). Ellagic acid present (Pterocarya), or absent (Juglans). Aluminium accumulation demonstrated (rarely), or not found (usually). Sieve-tube plastids S-type.

Geography, cytology. Holarctic, Paleotropical, and Neotropical. Temperate to tropical. Basically North temperate and subtropical, extending to India, Indochina, Malaysia and Andean South America - absent from Africa and Australia. X = 16.

Taxonomy. Subclass Dicotyledonae; Crassinucelli. Dahlgren’s Superorder Rosiflorae; Juglandales. Cronquist’s Subclass Hamamelidae; Juglandales. APG 3 core angiosperms; core eudicot; Superorder Rosanae; fabid; Order Fagales.

Species 50. Genera 8; Alfaroa, Carya, Cyclocarya, Engelhardtia, Juglans, Oreomunnia, Platycarya, Pterocarya.

Economic uses, etc. Valuable sources of edible nuts (walnut, pecan), and many valuable timber species (walnuts, hickory).


Let them say of me, ‘As jealous as Ford, that searched a hollow walnut for his wife’s leman.’
(‘Merry Wives’, iv., 2 — leman = lover)

(Of a proffered cap:) Why, ’tis a cockle or a walnut shell,
A knack, a toy, a trick, a baby’s cap:
Away with it! come, let me have a bigger.
(‘Taming of the Shrew’, iv., 2)

Illustrations. • Technical details: Juglans, Engelhardtia, Platycarya, Pterocarya. • Technical details: Platycarya (Lindley).

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: 19th October 2016.’.