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The families of flowering plants.                                                                                                                                                                

Urticaceae Juss.

                        

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Habit and leaf form. Shrubs, lianas, and herbs, or trees (a few); non-laticiferous and without coloured juice. ‘Normal’ plants. Plants non-succulent. With neither basal nor terminal aggregations of leaves. Self supporting, or climbing. Mesophytic. Conspicuously heterophyllous (e.g. Urtica pilea), or not heterophyllous (mostly). Leaves small to large; alternate, or opposite; when alternate, spiral; petiolate (usually), or sessile; non-sheathing; simple. Lamina entire (usually), or dissected (rarely); conspicuously asymmetric (sometimes), or not conspicuously asymmetric; when dissected, palmatifid; pinnately veined, or palmately veined; cross-venulate. Leaves stipulate (usually), or exstipulate (e.g. Parietaria). Stipules interpetiolar, or intrapetiolar; free of one another, or concrescent. Lamina margins entire, or serrate, or dentate. Leaves without a persistent basal meristem. Domatia occurring in the family (two genera); manifested as pockets.

General anatomy. Plants with laticifers (non-articulated, unbranched, in Urtica), or without laticifers (usually?).

Leaf anatomy. Stomata anomocytic, or anisocytic. Urticating hairs present (Urticeae), or absent.

Lamina dorsiventral. Cystoliths usually present. The mesophyll containing mucilage cells (commonly), or not containing mucilage cells. Minor leaf veins without phloem transfer cells (4 genera).

Stem anatomy. Young stems often tetragonal. Secretory cavities present, or absent; when present, with latex, or with mucilage. Cork cambium present; initially deep-seated, or superficial (usually). Nodes tri-lacunar. Internal phloem present (Myriocarpa), or absent. Secondary thickening developing from a conventional cambial ring (usually), or anomalous (Myriocarpa); from a single cambial ring. ‘Included’ phloem present (Myriocarpa), or absent. Xylem with vessels. Vessel end-walls simple. Vessels without vestured pits. Wood storied, or partially storied. Sieve-tube plastids S-type (without starch).

Reproductive type, pollination. Unisexual flowerspresent. Plants monoecious, or dioecious, or polygamomonoecious. Female flowers with staminodes (scalelike), or without staminodes. Gynoecium of male flowers vestigial (usually), or absent. Pollination anemophilous; mechanism conspicuously specialized (the filaments reflexing violently).

Inflorescence, floral, fruit and seed morphology. Flowers solitary (rarely), or aggregated in ‘inflorescences’. The ultimate inflorescence unit cymose. Inflorescences axillary; loose, glomerate, spiked, racemed, panicled or capitate cymes, the flowers often condensed into heads etc., or sometimes crowded on a common receptacle which may be concave or convex; with involucral bracts, or without involucral bracts. Flowers bracteate, or ebracteate; minute, or small; regular; (3–)4–5(–6) merous. Hypogynous disk absent.

Perianthsepaline, or vestigial to absent (sometimes, in female flowers); (2–)4–5(–6); free, or joined; 1 whorled; persistent; accrescent (often), or non-accrescent. Calyx (the perianth being thus interpreted) (2–)4–5(–6) (males), or 3–5 (when present, in females); 1 whorled; polysepalous, or gamosepalous; regular; persistent; accrescent, or non-accrescent; imbricate, or valvate.

Androecium (2–)4–5(–6). Androecial members free of the perianth; free of one another; 1 whorled. Androecium exclusively of fertile stamens. Stamens (3–)4–5(–6); isomerous with the perianth; oppositisepalous; inflexed in bud (uncoiling elastically); filantherous (the filaments usually wrinkled). Anthersdorsifixed; dehiscing via longitudinal slits; introrse; tetrasporangiate. Microsporogenesis simultaneous. The initial microspore tetrads tetrahedral, or decussate. Pollen grains aperturate; 2 aperturate, or 3 aperturate, or 7–15 aperturate; porate, or foraminate; 2-celled (in Parietaria,Pellionia and Urtica).

Gynoeciumostensibly 1 carpelled (i.e. with no obvious evidence of more than one carpel). Carpels reduced in number relative to the perianth. The pistil 1 celled. Gynoecium monomerous (ostensibly), or syncarpous (supposedly, theoretically); of one carpel (at least, usually with no evidence of syncarpy), or synstylovarious to eu-syncarpous (theoretically); superior (usually), or partly inferior (Pipturus, etc.). Carpel (if treated as monomeric) shortly stylate, or non-stylate; apically stigmatic; 1 ovuled. Placentationbasal. Ovary if recognised as syncarpous, 1 locular. Gynoecium stylate, or non-stylate to stylate. Styles 1. Stigmas 1 (usually), or 2 (e.g. Phenax); dry type; papillate; Group II type. Placentation if recognised as syncarpous, basal. Ovules in the single cavity 1; funicled, or sessile; ascending; non-arillate; orthotropous to hemianatropous; bitegmic; crassinucellate. Outer integument contributing to the micropyle, or not contributing to the micropyle. Embryo-sac development Polygonum-type. Polar nuclei fusing prior to fertilization. Antipodal cells formed; 3; proliferating, or not proliferating. Synergids pear-shaped. Hypostase present (in Urtica). Endosperm formation nuclear. Endosperm haustoria present; chalazal (short, in Urtica). Embryogeny asterad.

Fruit fleshy, or non-fleshy. The fruiting carpel (treated as monomeric) indehiscent; an achene, or nucular, or drupaceous. Fruit if recognised as syncarpous, indehiscent; achene-like, or a nut, or a drupe (rarely). The drupes with one stone. Gynoecia of adjoining flowers not forming a multiple fruit. Fruit 1 seeded. Seeds scantily endospermic, or non-endospermic. Endosperm oily, or not oily. Cotyledons 2. Embryo achlorophyllous (2/2); straight.

Physiology, biochemistry. Not cyanogenic. Alkaloids present, or absent. Iridoids not detected. Arthroquinones detected (Boehmeria); polyacetate derived. Proanthocyanidins present, or absent; when present, cyanidin. Flavonols present, or absent; when present, kaempferol and quercetin, or quercetin. Ellagic acid absent (8 species, 5 genera). Arbutin absent. Aluminium accumulation not found. C3. C3 physiology recorded directly in Parietaria, Pilea.

Geography, cytology. Temperate to tropical. Cosmopolitan except frigid zones. X = 6–14.

Taxonomy.Subclass Dicotyledonae; Crassinucelli. Dahlgren’s Superorder Malviflorae; Urticales. Cronquist’s Subclass Hamamelidae; Urticales. APG 3 core angiosperms; core eudicot; Superorder Rosanae; fabid; Order Rosales.

Species 550. Genera 49; Aboriella, Achudemia, Archiboehmeria, Astrothalamus,Australina, Boehmeria, Chamabainia, Cypholophus, Debregeasia,Dendrocnide, Didymodoxa, Discocnide, Droguetia, Elatostema,Forsskaolea, Gesnouinia, Gibbsia, Girardinia, Laportea,Lecanthus, Leucosyke, Maoutia, Meniscogyne, Myriocarpa,Nanocnide, Neodistemon, Neraudia, Nothocnide, Obetia,Oreocnide, Parietaria, Pellionia, Petelotiella, Phenax,Pilea, Pipturus, Poulzolzia, Procris, Rousselia,Sarcochlamys, Sarcopilea, Soleirolia, Touchardia, Urera,Urtica.

Economic uses, etc. Commercial cordage fibre (ramie) is obtained from Boehmeria nivea, a few (e.g. Pilea spp.) are grown as novelties, and nettles (Urtica spp.) constitute edible and quite palatable greens.

 Illustrations:

  • Technical details: Laportea (Thonner).
  • Technical details: Pilea, Parietaria.
  • Technical details: Urtica, Boehmeria.
  • Parietaria judaica (as P. diffusa): Eng. Bot. 1278, 1868.
  • Parietaria officinalis (B. Ent.).
  • Urtica dioica, U. urens and U. pilulifera: Eng. Bot. 1279, 1282 and 1280 (1868).
  • Urtica dioica (B. Ent.). 
  • Urtica pilulifera (B. Ent.).
  • Helxine (= Parietaria).
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