FLORA OF THE DISTRICT OF COLUMBIA. 197 



6. Tithymalopsis corollata (L.) Klotzsch & Garcke. Flowering spurge. 



Common in somewhat dry open places, roadsides, and fields. July-Oct. Eastern 

 N. Amer. {Euphorbia corollata L.) 



Variable in form of leaf, inflorescence, and appendages, and in amount of pubes- 

 cence 



6. POINSETTIA Graham. 



The poinsettia (P. pulcherrima Graham), with brilliant red upper leaves, is a well- 

 known houseplant, especially popular at Christmas time. 



1. Poinsettia dentata (Michx.) Small. 



Open places; Seven Locks and near Plummers Island. July-Sept. Pa. to Tex. 

 (Euphorbia dentata Michx.) 



7. TITHYMALTJS Adans. 



The name spurge is applied generally to all the plants of this and even related 

 genera, but more strictly belongs to T. lathyrus (L.) Hill, known also as caper spurge 

 and mole plant, a stout glaucous plant with linear-lanceolate leaves, sometimes 

 cultivated in gardens. 



Leaves serrulate; glands transversely oval; seeds lenticular, smooth or faintly reticu- 

 late. Winter annual; umbel 3-rayed; capsule warty 1. T. obtusatus. 



Leaves entire; glands crescent-shaped; seeds ovoid. 



Leaves obovate; umbel 3-rayed; seeds pitted; winter annual 2. T. commutatus. 



Leaves linear; umbel many-rayed; seeds smooth; perennial by buds on horizontal 

 roots 3. T. cyparissias. 



1. Tithymalus obtusatus (Pursh) Klotzsch & Garcke. 



Frequent locally in moist open woods. March-June. Eastern and southern U. S. 

 {Euphorbia obtusata Pursh; E. dictyosperma of Ward's Flora.) 



2. Tithymalus commutatus (Ehgelm.) Klotzsch & Garcke. 



Occasional in rich moist land, chiefly in woods, along the upper Potomac. March- 

 June. Eastern and southern U. S. {Euphorbia comviutata Engelm.) 



3. Tithymalus cyparissias (L.) Hill. Cypress spurge. 

 One colony on the campus at College Park; also found along the railroad near 



Laurel. May. Cultivated from Eur. and frequently naturalized in the northeastern 

 states. {Euphorbia cyparissias L.) 



Seeds rarely in the United States but commonly at College Park. 



91. CALIITRICHACEAE. Water starwort Family. 



" 1. CALLITRICHE L. Water starwort. 



Plants forming low tufts on moist soil; leaves uniform in shape, 3-nerved, crowded; 



fruit pedunculate. Bracts none 1. C. austini. 



Plants aquatic or sometimes growing on mud; leaves 1-nerved; fruit sessile. 

 Fruit with rather fugacious bracts at the base; emersed and submersed leaves 

 unlike. 



Fruitoval, flat on the face, longer than the styles 2. C. palustris. 



Fruit obovate, plano-convex, shorter than the styles 3. C. heterophylla. 



Fruit without bracts; all leaves submersed, linear 4. C. autumnalis. 



1. Callitriche austini Engelm. 



Occasional in damp shaded places. Fr. May-June. Eastern U. S. 



2. Callitriclie palustris L. 



In shallow, usually running water. Fr. May-Aug. Cosmopolitan. (C. verna L.) 



3. Callitriche heterophylla Pursh. 



In shallow water; Woodside and Hunting Creek. Fr. May-Aug. Eastern U. S. 



