Jones: Flora of Illinois, 43. Ulmaceae HI 



platanoides (Lam.) Sudw.} Swamp White Oak 



Q. bicolor Willd. 



43. Ulmaceae Mirb. — Elm Family 



I. Leaves with I principal vein from the base, the lateral veins straight, parallel, usually 



more than 10 pairs; flowers m clusters on twigs of the preceding season; twigs with 



solid pith. 



2. Flowers appearing before the leaves; fruit a 1 -seeded, flat, thin-winged samara; 



leaves usually doubly serrate 1. Ulmus 



2. Flowers appearing with the leaves; fruit nut-like, muricate; leaves simply serrate 

 2. Planera 



1. Leaves (at least when mature) with 3-5 veins from the base, the lateral veins curved, 

 fewer than 10 pairs; flowers borne on the twigs of the season, appearing with the 

 leaves; twigs with chambered pith; fruit a drupe; bark corky-ridged 3. Celtis 



I. Ulmus L. — Elm 



L Flowers drooping, on slender pedicels; calyx not ciliate; leaves gkbrous or 

 nearly so above; nut scabrous. 



2. Branches not corky-winged; buds glabrous or nearly so; fruit glabrous ex- 

 cept the ciliate margins; woods, very common. Apr. American or White 

 Elm U. americana L. 



2. Branches (at least some of them) usually more or less corky- winged; 

 fruit pubescent. 



3. Buds pubescent; leaves 5-13 cm. long; flowers racemose; woods, in the 

 n. half of the state, not common. Apr.-May. Rock Elm. \{J . race- 

 rnosa Thomas, not Borkh.} U. thomasi Sarg. 



3. Buds glabrous or nearly so; leaves 2-8 cm. long; flowers fascicled; hill- 

 sides, cliffs, ridges, s. 111. Apr. Winged Elm U. alata Michx. 



L Flowers nearly sessile in erect dense clusters; calyx ciliate; leaves scabrous 

 above; buds reddish-pubescent; branches not corky-winged; woods, com- 

 mon. Apr. Slippery Elm U. fulva Michx. 



2. Planera J. F. Gmel. 



P. aqiiatica [Walt.} J. F. Gmel. Water Elm. Swamps, s. 111., not common. 

 Apr.-May. A specimen without flowers or fruits collected at Mermet, July 18, 

 1928 (McDougdll 142), may be this species, but sterile specimens often close- 

 ly resemble smooth-branched material of Ulmus alata. 



3. Celtis L. — Hackberry 



1. Leaves sharply serrate; drupes 7-9 mm. in diameter at maturity; fruiting 

 pedicels longer than the petioles: nutlet brownish, 6-8 mm. long, obovoid, 

 pitted; tree, 10-20 m. tall; woods, usually near streams, common. Apr.- 

 May. [C. crassifolia Lam.] Hackberry C. occidentalis L. 



1. Leaves entire or nearly so; nutlet 5-6 mm. long, globose, pitted. 

 2. Leaves lanceolate, long-acuminate, usually broadly cuneate at base; fruit- 

 ing pedicels longer than the petioles; drupes 4-6 mm. in diameter; tree, 

 10-30 m. tall; woods and river banks, s. 111., in the valley of the 



