196 CONTRIBUTIONS FROM THE NATIONAL HERBARIUM. 



3. Chamaesyce preslli (Guss.) Arth. 



Common in cultivated fields and open waste places. May-Oct. Eastern N. Amer. 

 (Euphorbia hypericifolia of Ward's Flora; E. prcslii Guss.) 



The whole plant turns crimson in autumn. 



Dichrophyllum marginatum (Pursh) Klotzsch & Garcke, snow-on-the-mountain, is 

 sometimes found around gardens where it has been cultivated. Native of the western 

 U. S. (Euphorbia marginata Pursh.) 



5. TITHYMALOPSIS Klotzsch & Garcke. 

 The species of this genus, while generally distinct, often hybridize when they occur 

 together, and it is probable that the great variety of occasional intermediates, even 

 between such distinct species as T. corollata and T. ipecacuanhae, have arisen in this 

 way. The flowers are often replaced by a cauliflower-like gall. All the species vary 

 greatly in amount of pubescence, red color of stem and leaves, and form of leaf and 

 appendages. 



Main stem well developed, longer than the umbel; plants flowering in summer. 

 Leaves bright green, not much paler on the lower side, sessile or nearly so. 



T 5. T. corollata. 



Leaves dark green above, paler on the lower side, generally short-petioled, spreading 

 or drooping. Plant more pubescent, especially at the nodes. .4. T. paniculata. 

 Main stem nearly always shorter than the umbel, often subterranean; plants flowering 

 in spring or early summer. 

 Appendages of the involucral glands none or about half the width of the gland, 

 greenish. Plant entirely glabrous or very rarely with a few hairs at the nodes- 

 main stem below ground, the first flowers appearing at the surface. 



Appendages conspicuous, petal-like. L T ' i P ecacuanhae - 



Plants with a main stem 10-30 cm. long, the stems erect, often hairy at the nodes; 

 leaves lanceolate to ovate or, if oblong, broadest below the middle, darker on 

 the upper side; first flowers May to June 3. t. zinniiflora 



Plants branching from near the ground or, if with a longer main stem, then ascend"- 

 mg, not conspicuously more hairy at the nodes; leaves of many forms not 

 much darker above; first flowers April to May 2. T. marylandica. 



1. Tithymalopsis ipecacuanhae (L.) Small. WlLD IPECA0 

 Common in open places in the sandy soils east of Washington. Apr.-May Eastern 



U.S. (Euphorbia ipecacuanhae L.) 

 Very variable in leaf form and color. 



2. Tithymalopsis marylandica (Greene) Small. 



Rare in sandy land at Sunnyside and Seat Pleasant, but more frequent north of 

 our range toward Baltimore. May-July. (Euphorbia arundelana Bartlett- E maru- 

 landica Greene.) " 



■ ^ !*?* T/?™ intermed iate between T. ipecacuanhae and T. corollata are 

 included under this name, and it is possible that they all originated from crosses of 

 those species, as both occur with T. marylandica in nearly every place where it has 

 been found. 



Tithymalopsis mercurialina (Michx.) Small has been reported from our region but 

 probably erroneously. (Euphorbia mercurialina Michx.) 



3. Tithymalopsis zinniiflora Small. 



Rare in sandy land; College Park. June. Southeastern U. S. 



4. Tithymalopsis paniculata (Ell.) Small. 



Occasional, generally in sandy land; Plummers Island and Bladensburg. South- 

 eastern U. S. (Euphorbia paniculata Ell.) 



Specimens collected by Dewey at Glen Carlyn and by Knowlton at Laurel are 

 intermediate between this and T. corollata. 



