ALNUS 



Alnus, Linnaeus, Gen. PL 285 (1737); Bentham et Hooker, Gen. PL iii. 404 (1880); Winkler, in 



Engler, Pflanzenreich, iv. 61, Betulacece, 10 1 (1904). 

 Betula, Linnaeus, Gen. PL 485 (1764) (in part). 



Alna.sterz.vA Clethropsis, Spach, Ann. Sc. Nat. sir. 2, xv. 200, 201 (1841). 

 Semidopsis, Zumaglini, Fl. Pedem. i. 249 (1849). 

 Alnobetula, Schur, Verhatid. Siebenb. Ver. Naturw. iv. 68 (1858). 



Deciduous trees or shrubs, belonging to the order Betulaceae. Leaves alternate, 

 simple, stalked, usually serrate or dentate, rarely entire, penninerved. Stipules 1 

 enclosing the leaf in the bud, caducous or deciduous. Flowers opening either 

 in early spring before or with the unfolding of the leaves, or in two species in 

 autumn, monoecious, unisexual, without petals, in few - flowered cymes in the 

 axils of short - stalked peltate scales of pedunculate catkins. Staminate catkins, 

 at first naked and erect, afterwards pendulous, in the axils of the last leaves or of 

 leafy bracts ; scales three-flowered ; bracteoles, three to five, adnate to the base 

 of the scale ; calyx, four-partite ; stamens four, filaments short, undivided ; anthers 

 dorsi-fixed, not pilose at the apex. Pistillate catkins erect, solitary or racemose, in 

 the axils of the leaves and produced in autumn, or terminal on a short leafy branch 

 and produced in spring ; scales two-flowered ; bracteoles, two to four, adnate to the 

 base of the scales ; calyx absent ; ovary two-celled ; styles two, stigmatose at the 

 apex ; ovule, solitary in each cell, suspended. Fruit, a strobile or cone, formed by 

 the scales of the pistillate flower becoming, when ripe, thick, woody, obovate, three- 

 to five-lobed or truncate at the thickened apex. Cones persistent on the branch 

 after the opening of the closely imbricated scales and the escape of the nutlets. 

 Nutlet, compressed, minute, bearing at the apex the remains of the styles, marked at 

 the base by a scar, with or without lateral wings. Seed, solitary by abortion, filling 

 up the cavity of the nutlet. 



About twenty-five species are distinguished, inhabiting Europe, Algeria, extra- 

 tropical Asia, North America, Central America, and the Andes of South America 

 from Colombia to Peru. 



The following key includes all the species in cultivation, with the exception of 

 Alnus serrulata, Willdenow, a North American shrub. 



I. Buds sessile, with several {two to six) outer scales, which are unequal in length. 

 1. Alnus firma, Siebold et Zuccarini. Japan. See p. 952. 



1 Cf. Lubbock, "On Stipules of the Alder," m/otirn. Linn. Soc. (Bol.), xxx. 527 (1895). 



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