PLATANACE3!. 297 



deltoidly ovate, acute, cordate at base, 3—5 in. long, ascending or spread- 

 ing on stoutish petioles 1 — 1% in. long: sepals broadly ovate, little 

 exceeding the broadly ovate, minutely punctate achene which is little 

 more than % line long, — Borders of thickets near streamlets on the sea- 

 ward slope of the Coast Eange in San Mateo Co., and no doubt all the 

 middle Oalifornian " U. Lyallii " is this. June, July. 



3. U. holosericea, Nutt. Not only stinging-bristly, but also densely 

 and finely hoary-tomentose, especially on the leaves beneath: stems very 

 stout, 5—8 ft. high: leaves oblong- to ovate-lanceolate, acuminate, 2—4 

 in. long, often subcordate at base; stipules oblong, % in. long: inner 

 sepals ovate, densely hispid, J^ line long, about equalling the broad- 

 ovate achene. — Very common on banks of streams, and in other moist 

 places. 



2. HESPEROCNLDE, Torr. Very analogous to Urtica urens, but gen- 

 erically separated on account of the complete cohesion of the sepals of the 

 pistillate flower into a membranous compressed oblong-ovate sac, with 

 a minutely 2 — 4-toothed orifice. 



1. H. tenella, Torr. Slender, 1 — 2 ft. high, hispid with branching 

 hairs and bristly: leaves ovate, % — X% in. long, short-petioled, thin, 

 obtusely serrate: flower-clusters lax, shorter than the petioles: perianth 

 hispid with hooked hairs, J£ — %. line long in fruit: achene thin, minutely 

 striate-tuberculate. — Shady banks in Napa and Contra Costa counties 

 and southward. April, May. 



Ordeb lxxxi. PLATANACE/E, 



Eepresented by one species, of the only genus, 



1. PLAT ASUS, Theophr. Monoecious trees, with exfoliating bark, 

 ample palmately lobed leaves, sheathing deciduous stipules, and flowers 

 in dense globose naked heads, without perianth, but subtended by 

 clavate truncate minute hairy scales. Filaments very short; anthers 

 clavate, with prolonged peltate connective. Style stigmatic on one side, 

 persistent; ovules 1 or 2, pendulous. Fruit an obpyramidal achene. 



1. P. racemosa, Nutt. Tree widely branching, often 60—80 ft. high: 

 leaves broadly cordate, 3— 5-lobed, densely rusty- tomentose when young; 

 lobes acute or acuminate, sometimes toothed: fertile heads 2 — 7, in a 

 moniliform spike; in fruit 1 in. in diameter. — Along all large streams. 



Obdbb lxxxii. BETULACE>E. 



Of Betula, the principal genus no species occurs within our limits; 

 though Alnus, the only other genus of the order, is with us. 



1. ALNUS, Pliny (Alder). Ours monoecious deciduous trees, inhab- 

 iting stream banks or other wet places among the hills. Bark smooth. 



