FLORA OF THE DISTRICT OF COLUMBIA. 211 



20. Viola papilionacea Pursh. Butterfly violet. 



In all kinds of situations; very abundant; our commonest violet. Apr.-May. East- 

 ern U. S. (F. domestica Bic knell; V.familiaris Greene; V. cucullata of Ward's Flora; 

 V. communis Pollard.) 



The types of V./amiliaris and V. communis are from our region. 



Viola papilionacea X hirsutula Brainerd. 



Collected at several scattered stations. Leaves in outline intermediate between 

 those of the parents, with the pubescence of V. hirsutula. ( V. papilionacea X villosa 

 Pollard, the type from Darlecarlia Reservoir.) 



Viola papilionacea X sagittata Brainerd. 



Darlecarlia Reservoir and Takoma Park. Leaves regularly toothed, narrower 

 than in V. papilionacea. ( V. conjugens Greene.) 



Viola papilionacea X sororia Brainerd. 



Collected at several scattered stations. Leaves like those of the parents, but only 

 very slightly pubescent. ( V. grandis Greene; V. induta Greene.) 



The type localities of V. grandis and V. induta are within our region. 



Viola papilionacea X triloba Brainerd. 



Common with the parents. Leaves less deeply lobed than in V. triloba, more or 

 less pubescent. 



107. PASSIFLOEACEAE. Passion-flower Family. 



1. PASSIFLOKA L. Passion-flower. 



Passiflora incamata L., maypops or maracocks, is cultivated within our limits, 

 usually trained over trellises and pergolas. Native from central Va. southward. 



1. Passiflora lutea L. 

 Common in thickets, especially along the Potomac. May-Aug. Southeastern U. S. 



108. CACTACEAE, Cactus Family. 



1. OPTJNTIA Mill. 

 1. Opuntia vulgaris Mill. Prickly pear. 



Rocky or sandy soil; Plummers Island and Great Falls. June. Eastern U. S. 

 (0. opuntia Karst.) 



A tuft of plants in fruit is shown in plate 34B. 



109. DAPHNACEAE. leatherwood Family. 



1. DmcA L. 



1, Dirca palustris L. Leatherwood. Moosewood. 



Low places along the Potomac. Apr. Eastern U.S. 



110. LYTHEACEAE. loosestrife Family. 



Calyx tube short, campanulate or hemispheric. Flowers regular. 

 Leaves opposite; Howers small, solitary or few; petals 4; low annual herbs. 



1. ROTALA. 

 Leaves mostly whorled; flowers large, densely clustered; petals 5 (rarely 4); large 



aquatic perennial herbs 2. DECODON. 



Calyx tube cylindric or tubular. 

 Flowers regular; calyx tube symmetric; plants perennial, not viscid-hairy. 



3. LYTHRUM. 



Flowers irregular; calyx tube spurred or enlarged on one side at base; plants annual, 



viscid-hairy 4. PARSONSIA. 



