CLASS XXI. ORDER V. 367 



378. ALNUS. 

 Alnus serrui.ata. Willd. Common Alder. 



Leaves obovate, acuminate, the veins and their axils 

 hairy underneath ; stipules elliptical, obtuse. Willd. 

 Syn. Betula serrulata. Ait. 



The Alder grows in wet grounds, and forms large thickets in 

 swamps and about the edges of streams and ponds. Considered 

 as a tree it ranks with those of the smallest size. Its leaves are 

 oval or inversely ovate, serrate, acute, or slightly acuminate, fur- 

 nished underneath with prominent, parallel, hairy veins. Bar- 

 ren aments pendulous, each scale containing about three flowers 

 which have four petals and four stamens. Fertile ones short, 

 rigid, forming a persistent cone. — March, April. 



Alnus Glauca. Mx. f. Glaucous Alder. 



Leaves roundish, elliptical, doubly serrate, glaucous 

 underneath. 

 Syn. Alnus incana. Willd. 



Michaux thinks this species to be about a third taller than the 

 preceding. It is distinguishable at sight by its larger and coarser 

 leaves, which are of a pale bluish green underneath. — Swamps. 

 — West Cambridge and elsewhere. — April. 



PENTANDRIA. 



379. XANTHIUM. 

 Xanthium strumarium. L. Sea Burdock. 



Stem unarmed ; leaves heart shaped, three nerved. 

 L. 



A very rough plant, growing at the edges of beaches, &c., 

 near the salt water. Stem erect, spotted, bristly. Leaves hard 

 and rough like a file, heart shaped, serrate, on long petioles. 

 The fruit is an oval burr, or nut of two cells, covered with stiff 

 thorns, and ending in a pair of strong points, like horns. — 

 August. 



