The World Flora Online

SELECTED REFERENCES

Bassett, I. J., C. W. Crompton, and D. W. Woodland. 1974. The family Urticaceae in Canada. Canad. J. Bot. 52: 503-516. I. Friis. 1993. Urticaceae. In: K. Kubitzki et al., eds. 1990+. The Families and Genera of Vascular Plants. 2+ vols. Berlin etc. Vol. 2, pp. 612-630. Kingsbury, J. M. 1964. Poisonous Plants of the United States and Canada. Englewood Cliffs. Miller, N. G. 1971. The genera of the Urticaceae in the southeastern United States. J. Arnold Arbor. 52: 40-68. Weddell, H. A. 1856. Monographie de la Famille des Urticacées. Paris. Woodland, D. W. 1989. Biology of temperate Urticaceae (nettle family). In: P. R. Crane and S. Blackmore, eds. 1989. Evolution, Systematics, and Fossil History of the Hamamelideae. 2 vols. Oxford. Vol. 2, pp. 309-318. [Syst. Assoc. Special Vol. 40A, B.]

Herbs or small shrubs [lianas, trees], herbs annual or rhizomatous perennial, usually pubescent, sometimes with stinging hairs, deciduous. Leaves opposite or alternate and spirally arranged, simple; stipules present or absent; petioles present. Leaf blades paired, equal in size (except in Pilea , which may have unequally paired leaves), dotted with linear or rounded marks formed by cystoliths (variously shaped calcium carbonate crystals inside epidermal cells). Inflorescences axillary or terminal, of paniculately or racemosely arranged cymes, or spikelike. Flowers bisexual or unisexual (staminate or pistillate), staminate and pistillate flowers on same or different plants; perianth hypogynous. Staminate flowers usually pedicellate; tepals 4-5, white or green; stamens 4-5, equaling tepals in number; filaments inflexed in bud, reflexing suddenly as flowers open; anthers basifixed, dehiscing by longitudinal slits; pollen ejected explosively; pistillode 1. Pistillate flowers usually sessile; tepals 2-4, hypogynous, greenish or reddish, distinct or connate; staminodes present or absent; pistil1, 1-locular; placentation basal; ovule1; style present or stigma sessile; stigma linear [capitate]; Bisexual flowers: tepals 4; stamens4; pistil1. Fruits achenes, free or loosely or tightly surrounded by persistent, accrescent perianth.

Herbes, arbustes ou lianes monoïques ou dioïques, dressés, rampants ou grimpants, munis de poils spécialisés urticants injectant un liquide brûlant au toucher (seulement dans la tribu des Urticeae ; voir la note ci-dessous consacrée à leur structure et leur fonction) ; glabres, pubérulents ou pubescents, souvent avec des poils raides et pointus, pouvant être crochus, mais non urticants ; cystolithes présents dans les cellules de l’épiderme, ponctiformes, allongés ou linéaires. Stipules latérales ou intrapétiolaires, soudées. Feuilles alternes ou opposées, simples, souvent inégales (anisophylles) ; pétiole présent ou presque nul ; limbe symétrique ou non, jamais lobé (au Gabon), base cunéée à tronquée ou cordée, sommet généralement aigu à acuminé, cartacé à coriace, parfois un peu charnu, vert sombre à vert pâle, glabre, pubérulent, pubescent ou à pilosité blanche, tomenteuse, parfois avec des poils urticants (tribu des Urticeae), marge entière, crénulée, crénée ou diversement dentée ; cystolithes généralement nombreux sur la face supérieure ; nervation symétriquement ou asymétriquement triplinerve (la médiane est flanquée de deux nervures latérales basales subégales), la paire de ces deux nervures latérales atteignant entre ½ et 4/5 du sommet du limbe, les latérales supérieures plus lâches, nervation tertiaire scalariforme ou réticulée. Inflorescences axillaires, en cymes ou en racèmes pédonculés ou sessiles, lâches ou condensées, à fleurs en petits glomérules cymeux ou condensés. Fleurs minuscules, unisexuées ou (hors Gabon) parfois bisexuées, actinomorphes ou fleurs femelles parfois zygomorphes ; pédicelle généralement articulé sous le périanthe ; tépales 3 à 5, en un seul cycle, comparables ou de taille et de forme différente, libres ou soudés à la base. Fleurs mâles : étamines en nombre égal aux tépales ou (hors Gabon) solitaires, toujours infléchies en bouton et se dépliant brusquement et élastiquement à l’anthèse, dispersant ainsi activement le pollen ; pistillode souvent présent. fleurs femelles : tépales souvent inégaux, souvent accrescents après la pollinisation, ou (hors Gabon) rarement rudimentaires ou absents ; staminodes (uniquement dans la tribu des Elatostemeae) squamiformes et éjectant l’akène en se dépliant ; ovaire supère, généralement comprimé latéralement, souvent oblique ou asymétrique, uniloculaire, à placentation basale, ovule solitaire dressé ; style unique (trifide dans une espèce de Laportea), long ou presque nul, stigmate linéaire, capité ou pénicillé. Fruits : akène, parfois entouré par le périanthe persistant, accrescent et pouvant devenir charnu. Graine toujours solitaire, remplissant l’akène, testa mince ; albumen réduit ; embryon important, remplissant presque la graine (non toujours connu).

Les espèces des Urticaceae ont été souvent utilisées dans la production de fibres textiles, en vannerie, de ficelle et de corde, mais hormis l’introduction de Boehmeria nivea pour la production de fibres, des usages cités du Gabon sont vraiment limités. Ailleurs, des fibres sont aussi extraites d’espèces de Laportea et d’Urera. Des jeunes feuilles de nombreuses espèces peuvent être utilisées comme plantes potagères ou dans des soupes.

Famille d’environ 50 genres et 1000 espèces ; pratiquement cosmopolite, mais plus abondante sous les tropiques, dans des milieux humides. Au Gabon, cinq genres et 15 espèces ; mais dans les pays voisins, six espèces de plus qu’on pourrait aussi trouver au Gabon (et qui sont incluses dans les clés ci-dessous) et pas d’endémiques, bien que Urera gabonensis soit restreinte au Gabon et à la région forestière du sud du Cameroun.

Herbes , arbustes, lianes ou petits arbres, monoïques ou dioïques, sans latex, à cystolithes, pourvus souvent de poils urticants, à feuilles simples, alternes ou opposées, stipulées, souvent trinerves.'Fleurs'1-sexuées, rarement ☿, réunies en cymes souvent contractées, groupées en panicules, en épis ou en capitules; périgone ♂ (ou ☿), en général actinomorphe, à 4-5, rarement 3 segments, parfois en forme de cornet; étamines 4-5 (ou 3) opposées aux segments, parfois 1 seule, à filaments recourbés vers l'intérieur dans le bouton, se redressant brusquement au moment de l'anthèse, avec projection du pollen; ovaire avorté ordinairement bien apparent; périgone ♀ souvent très différent du ♂, à segments inégaux libres, ou soudés entre eux à la base ou réunis en un tube ou un utricule enveloppant l'ovaire, parfois nul; ovaire ovoïde ou lenticulaire, dressé ou réfléchi, surmonté d'un seul stigmate couvert de papilles souvent très longues; ovule dressé, orthotrope.'Fruit : akène ou drupe, souvent enveloppé du périgone accrescent, sec ou charnu.\n\t\t\tFamille comportant environ 40 genres et près de 1000 espèces, nombreuses surtout dans les pays chauds; au Congo belge, 13 genres et 43 espèces, dont 5 ou 6 douteuses ou mal connues.\n\t\t\tLa presque totalité des Urticacées congolaises existe dans l'Est de la Colonie, spécialement dans le District des Lacs Édouard et Kivu et la partie limitrophe du District Forestier Central; beaucoup même ne se trouvent que dans cette région (genres'Pilea, Elatostema, Parietaria, Droguetia ) et, la plupart, à des altitudes comprises entre 1500 et 2500 m; les'Parietaria'dépassent 3000 m et seul'P. ruwenzoriensis atteint l'étage alpin. Le Mayumbe, le Bas-Congo et le Kasai, au contraire, n'en comptent que six dont Urera cameroonensis à très vaste distribution et les ubiquistes cités plus bas.\n\t\t\tQuant à leur distribution en Afrique, on constate, abstraction faite des espèces douteuses, que sur les 38 Urticacées congolaises, 17 sont des espèces guinéennes dont 10 atteignent l'Angola, 11 s'étendent jusqu'au Kenya et au Territoire du Tanganyika et 2 ( Boehmeria et Procris) gagnent l'Asie tropicale et la Malaisie. C'est cependant avec l'Afrique orientale que les rapports sont les plus étroits : 27 de nos espèces s'y retrouvent dont 8 atteignent l'Abyssinie et une (Droguetia iners), l'Arabie et les Indes.\n\t\t\tLa famille est remarquable par l'uniformité du port (type urticoïde) à travers de nombreux genres, et sa systématique en est d'autant plus difficile que les fleurs sont extrêmement petites et presque toujours diclines, et qu'il existe une grande variabilité des organes végétatifs. Chez beaucoup d'espèces congolaises, la répartition des sexes (monœcie, diœcie, polygamie) et la place où apparaissent, chez les espèces monoïques, les fleurs ♂ et ♀, sont mal connues et devraient être étudiées sur le vif, ainsi que la succession dans le temps des fleurs des deux sexes (protandrie, protogynie? et la prédominance numérique, parfois étrangement marquée, de l'un ou l'autre.\n\t\t\tLes Urticacées jouent un rôle assez secondaire dans la végétation congolaise : certaines (genre'Urera ) sont des lianes ne comptant ni parmi les plus communes, ni parmi les plus puissantes; d'autres, les plus nombreuses, sont des éléments assez constants du sous-bois des forêts hygrophiles, plus rarement des épiphytes (genres'Pilea, Elatostema, Laportea, Procris, Droguetia ), d'autres enfin sont remarquablement ubiquistes ( Boehmeria , certains'Fleurya ) et quelques-unes sont devenues des « mauvaises herbes » extrêmement répandues dans les stations modifiées par l'homme, avec un caractère rudéral et nitrophile parfois très marqué ( Fleurya aestuans'et'Pouzolzia guineensis'partout,'Girardinia'et'Urtica dans l'Est).\n\t\t\tAu point de vue éthologique, il faut signaler la dispersion explosive du pollen par la détente brusque des étamines au moment de l'anthèse, remarquable surtout chez'Fleurya podocarpa . La dissémination des akènes se fait mécaniquement, dans les genres'Pilea'et'Elatostema , par la détente des staminodes recourbés et engagés en dessous du fruit, alors que celle des Urera est assurée par les oiseaux qu'attire le périgone accrescent, devenu charnu et d'un rouge vif à la maturité de l'akène. Chez'Fleurya podocarpa , au contraire, il y a géocarpie, une partie des akènes se produisant sur les rhizomes. Mais la particularité la plus remarquable des Urticacées réside dans les poils urticants spéciaux à la tribu des Urereae : tantôt très abondants, tantôt très rares et localisés sur les inflorescences, ils sont dans quelques-unes de nos espèces ( Urtica, Laportea, Girardinia ) assez robustes pour traverser les vêtements et assez toxiques pour causer de durables malaises : de telles orties rendent très pénible la traversée des forêts où, comme dans certaines vallées du Ruwenzori, elles forment un épais sous-bois.

Seed mostly with endosperm and a straight embryo Herbs, undershrubs, or rarely soft-wooded trees, rarely climbing, often armed with stinging hairs; epidermal cells mostly with prominent cystoliths; stems often fibrous Petals absent Male flowers with a 4–5-lobed calyx, lobes imbricate or valvate Flowers very small, unisexual, usually cymose, sometimes crowded on a common enlarged receptacle Leaves alternate or opposite, simple; stipules present or absent Female calyx like that of the male, often enlarged in fruit Staminodes scale-like or absent Stamens as many as and opposite the calyx-lobes; filaments inflexed in bud; anthers 2-celled Rudimentary ovary usually present Ovary free or adnate to the calyx, 1-celled; style simple; ovule solitary, erect Fruit a dry achene or fleshy drupe Herbs, undershrubs, or rarely soft-wooded trees, rarely climbing, often armed with stinging hairs; epidermal cells mostly with prominent cystoliths; stems often fibrous Petals absent Male flowers with a 4–5-lobed calyx, lobes imbricate or valvate Flowers very small, unisexual, usually cymose, sometimes crowded on a common enlarged receptacle Leaves alternate or opposite, simple; stipules present or absent Female calyx like that of the male, often enlarged in fruit Staminodes scale-like or absent Stamens as many as and opposite the calyx-lobes; filaments inflexed in bud; anthers 2-celled Rudimentary ovary usually present Ovary free or adnate to the calyx, 1-celled; style simple; ovule solitary, erect Fruit a dry achene or fleshy drupe

Inflorescences are extremely varied, mostly cymose, often of densely clustered flowers, and subtended by involucral bracts; occasionally the inflorescence axis is contracted into a flattened, disk-shaped, fleshy receptacle Flowers minute, unisexual, actinomorphic or (especially the female flowers) zygomorphic, with one whorl of tepals or rarely the female flowers naked, sessile or pedicellate, pedicel often articulated just below the perianth Male flowers with (1)2–5 tepals; stamens equal in number and opposite the tepals or solitary, inflexed in bud until reflexing suddenly to forcibly eject the pollen; anthers 2-thecous opening by longitudinal slits; rudimentary ovary usually present Female flowers with 3–5 tepals, which are free or united, often very unequal, often accrescent after pollination, rarely absent; staminodes, when present, scale-like, inflexed (sometimes actively ejecting the achene when ripe); ovary superior, syncarpous, erect, usually somewhat laterally compressed, symmetrical or asymmetrical, glabrous, 1-celled, with 1 erect basal ovule (placenta absent or very small); style usually absent or very short; stigma capitate, brush-like, or linear Fruit an achene, consisting of the hardened ovary-wall, often enclosed by the persistent accrescent perianth Seed with a thin membranaceous testa, usually not fused to the endocarp, mostly with little or no endosperm, and the cotyledons correspondingly swollen and fleshy Cystoliths (incrustations of calcium or cellulosis most easily visible in dried material) are generally present in the epidermal cells, dot-like, elongated, or linear Leaves alternate or opposite, petiolate or sessile, sometimes the opposite leaves are anisophyllous with each of a pair of leaves unequal in shape and/or size; stipules usually present, lateral or often intrapetiolar, often fused; lamina simple to deeply 3–5-lobed, rarely 7-lobed, margin entire, serrate or dentate, usually strongly 3-nerved from the base with much smaller lateral nerves from the midnerve, or sometimes evenly penninerved Annual or perennial herbs, shrubs, lianas, or small trees with soft wood; monoecious or dioecious (rarely polygamous); stinging hairs are present in some genera while stiff, non-stinging hairs (without bulbous tip, sack-like base and irritating fluid) are frequent Stinging hairs are large, unicellular and have a calcified wall, bulbous tip, and a soft-walled, sack-like lower part; the bulbous tip is easily detached, liberating an irritating fluid from the sack-like part; the sack-like base of the stinging hairs is embedded in, or occasionally mounted on, a small epidermal protuberance on stems, petioles or inflorescences, see Tab. 23 Flowers minute, unisexual, actinomorphic or (especially the female flowers) zygomorphic, with one whorl of tepals or rarely the female flowers naked, sessile or pedicellate, pedicel often articulated just below the perianth Male flowers with (1)2–5 tepals; stamens equal in number and opposite the tepals or solitary, inflexed in bud until reflexing suddenly to forcibly eject the pollen; anthers 2-thecous opening by longitudinal slits; rudimentary ovary usually present Female flowers with 3–5 tepals, which are free or united, often very unequal, often accrescent after pollination, rarely absent; staminodes, when present, scale-like, inflexed (sometimes actively ejecting the achene when ripe); ovary superior, syncarpous, erect, usually somewhat laterally compressed, symmetrical or asymmetrical, glabrous, 1-celled, with 1 erect basal ovule (placenta absent or very small); style usually absent or very short; stigma capitate, brush-like, or linear Fruit an achene, consisting of the hardened ovary-wall, often enclosed by the persistent accrescent perianth Seed with a thin membranaceous testa, usually not fused to the endocarp, mostly with little or no endosperm, and the cotyledons correspondingly swollen and fleshy Cystoliths (incrustations of calcium or cellulosis most easily visible in dried material) are generally present in the epidermal cells, dot-like, elongated, or linear Leaves alternate or opposite, petiolate or sessile, sometimes the opposite leaves are anisophyllous with each of a pair of leaves unequal in shape and/or size; stipules usually present, lateral or often intrapetiolar, often fused; lamina simple to deeply 3–5-lobed, rarely 7-lobed, margin entire, serrate or dentate, usually strongly 3-nerved from the base with much smaller lateral nerves from the midnerve, or sometimes evenly penninerved Annual or perennial herbs, shrubs, lianas, or small trees with soft wood; monoecious or dioecious (rarely polygamous); stinging hairs are present in some genera while stiff, non-stinging hairs (without bulbous tip, sack-like base and irritating fluid) are frequent Stinging hairs are large, unicellular and have a calcified wall, bulbous tip, and a soft-walled, sack-like lower part; the bulbous tip is easily detached, liberating an irritating fluid from the sack-like part; the sack-like base of the stinging hairs is embedded in, or occasionally mounted on, a small epidermal protuberance on stems, petioles or inflorescences, see Tab. 23

Fls unisexual or rarely perfect; cal 3–5-lobed or parted, usually more deeply so in the staminate fls, or the sep distinct; pet none; stamens as many as the cal-lobes and opposite them, inflexed in bud, elastically reflexed when the pollen is shed; ovary superior, unilocular, with a single erect, orthotropous ovule from the base; style 1; fr usually an achene, often enclosed in an accrescent cal; seeds with straight, dicotyledonous embryo and usually a thin endosperm; herbs (ours) with opposite or alternate, simple, usually (except in Parietaria) stipulate lvs and axillary (in ours), simple or branched clusters of inconspicuous small fls. 45/700.

Herbs, subshrubs, or shrubs, rarely trees, very rarely climbing, stems often fibrous, sometimes succulent. sometimes armed with stinging hairs; epidermal cells of leaves, sometimes stems, perianths mostly with prominent cystoliths punctiform to linear; Leaves alternate or opposite, stipules present, rarely absent; leaf blade simple. Inflorescences cymose, paniculate, racemose, spicate, or cluster-capitate, usually formed from glomerules, sometimes crowded on common enlarged cuplike or discoid receptacle, rarely reduced into a single flower. Flowers unisexual (plants monoecious or dioecious), rarely bisexual in partial flowers; actinomorphic, very small, (1-)4- or 5-merous, rarely perianth absent in female flowers. Calyx absent. Perianth lobes imbricate or valvate. Male flowers: stamens as many as and opposite to perianth lobes, filaments inflexed in bud; anthers 2-locular, opening lengthwise, rudimentary ovary often present. Female flowers: perianth lobes free or connate, usually enlarged in fruit and persistent, occasionally absent; staminodes scarious, opposite to the perianth lobes, or absent. Ovary rudimentary in male flowers, sessile or shortly stipitate, free or adnate to the perianth; 1-locular, ovule solitary, erect from the base; style simple, or absent; stigma diverse, capitate, penicillate-capitate (brushlike), subulate, filiform, ligulate, or peltate. Fruit usually a dry achene, sometimes a fleshy drupe, often enclosed by the persistent perianth. Seed solitary, endosperm usually present; embryo straight; cotyledons ovate elliptical or orbicular.

Leaves alternate or opposite, sometimes anisophyllous, petiolate or sessile; stipules usually present, lateral or often intrapetiolar, often fused; lamina simple or 3–5(–7)-lobed, margin entire or variously dentate, usually with 3 subequal nerves from the base, the basal pair of nerves reaching towards the leaf-apex, the other lateral nerves usually weaker and shorter, cystoliths usually clearly visible in the epidermis of the upper surface Inflorescences very varied, mostly pedunculate, lax or condensed racemes, often with flowers in small cymose glomerules, or sessile and condensed cymes in leaf-axils, partial inflorescences often subtended by involucral bracts, the inflorescence-axis sometimes flattened into a disc-shaped, ± fleshy receptacle Flowers minute, unisexual or rarely bisexual, actinomorphic or (especially in ? flowers) zygomorphic, with single whorl of tepals or rarely the ? flowers naked, pedicel often articulated below perianth Male flowers with (l–)2–5(–6) tepals, free or connate in lower half; stamens equalling tepals in number or solitary, always inflexed in bud; rudimentary ovary often present Female flowers with 3–5 tepals, free or ± completely united, often very unequal, often accrescent after pollination, rarely rudimentary or completely absent; staminodes, if present, rudimentary or scale-like and important for the dispersal of the fruit (ejecting the achene when reflexing); ovary superior, usually laterally compressed, often oblique or asymmetrical, unilocular, unicarpellate, placentation basal, with 1 erect ovule; stigma capitate, penicillate or filiform, linear Fruit an achene, sometimes enclosed by persistent accrescent perianth which may become fleshy Herbs, shrubs, lianas or small trees, monoecious, dioecious or rarely polygamous, some genera with stinging hairs, but also frequently with stiff non-stinging hairs, which may be curled or sharply hooked; usually with punctiform, elongated or linear cystoliths in epidermal cells Inflorescences very varied, mostly pedunculate, lax or condensed racemes, often with flowers in small cymose glomerules, or sessile and condensed cymes in leaf-axils, partial inflorescences often subtended by involucral bracts, the inflorescence-axis sometimes flattened into a disc-shaped, ± fleshy receptacle Flowers minute, unisexual or rarely bisexual, actinomorphic or (especially in ? flowers) zygomorphic, with single whorl of tepals or rarely the ? flowers naked, pedicel often articulated below perianth Male flowers with (l–)2–5(–6) tepals, free or connate in lower half; stamens equalling tepals in number or solitary, always inflexed in bud; rudimentary ovary often present Female flowers with 3–5 tepals, free or ± completely united, often very unequal, often accrescent after pollination, rarely rudimentary or completely absent; staminodes, if present, rudimentary or scale-like and important for the dispersal of the fruit (ejecting the achene when reflexing); ovary superior, usually laterally compressed, often oblique or asymmetrical, unilocular, unicarpellate, placentation basal, with 1 erect ovule; stigma capitate, penicillate or filiform, linear Fruit an achene, sometimes enclosed by persistent accrescent perianth which may become fleshy Herbs, shrubs, lianas or small trees, monoecious, dioecious or rarely polygamous, some genera with stinging hairs, but also frequently with stiff non-stinging hairs, which may be curled or sharply hooked; usually with punctiform, elongated or linear cystoliths in epidermal cells