Houstonia RUBIACEAE 871 



Flowers axillary, sessile or nearly so. 



Plant and capsule pubescent 8471. Diodia, p. 873. 



Plant and capsule glabrous 8475. Spermacoce, p. 874. 



Leaves in whorls of 4 to 8 8486. Galium, p. 874. 



8141. HOUSTONIA L. Houstonia 



Flowers solitary on filiform peduncles usually 2-5 cm long 1. H. caerulea. 



Flowers cymose or in small clusters, peduncles shorter than those of the preceding. 

 Fruit (when mature) conspicuously broader than long; sepals mostly 3-6 mm long; 



leaf blades ovate, lanceolate or narrow-lanceolate 2. H. purpurea. 



Fruit (when mature) not conspicuously broader than long; leaf blades of the stems 

 linear to narrow-oblong. 

 Calyx lobes about 1 mm long, usually shorter than the mature capsule; leaves 

 linear; capsule free only at the apex; stems tufted, from a hard or woody root. 



3. H . angusti folia. 



Calyx lobes usually more than 2 mm long, longer than the mature capsule; leaves 



linear or narrow-oblong; stems not from a woody root. 



Stem leaves linear to narrow-oblong, more or less glabrous, sometimes the blades 



rough-pubescent all over, in lines or only the margins roughened, regularly 



ciliate, but the radical leaves narrowly oval or oblong, the margins not 



regularly ciliate 4. H. longifolia. 



Stem leaves few and distant (the lower internode sometimes 5 cm long), rather 

 thick, obscurely 1-nerved, oblanceolate or linear-oblong, the radical ones 

 oval or oblong-spatulate, tapering into a petiole, ciliate, sometimes all of 

 the leaves ciliate on the margins (rough-pubescent margins of leaves must 

 not be confused with ciliate margins). (See excluded species no. 579, p. 

 1091 ) H. canadensis. 



1. Houstonia caerulea L. Bluets. Map 1906. Mostly in the north- 

 western and southeastern parts of the state. This species prefers a slightly 

 acid soil and is usually found in black, sandy soil in woodland or pastures 

 in the northwestern part of the state, and in open woodland and fallow 

 fields in the southeastern part of the state. Where it is found it is usually 

 common, sometimes covering acres. 



N. S. to Ont. and Wis., southw. to Ga., Ala., and Mo. 



2. Houstonia purpurea L. MOUNTAIN HOUSTONIA. Map 1907. My spec- 

 imens are mostly from the southern half of the state where it is more or 

 less frequent and occurs mostly on slopes in white and black oak woods. 

 In the northern part of the state it has been reported from Cass, Kos- 

 ciusko, Lake, and Tippecanoe Counties. 



This species, like Houstonia longifolia, is extremely variable. I have 

 specimens with the leaves varying from narrowly lanceolate to broadly 

 ovate. The calyx lobes vary from 3-6 mm in length. The plant that has the 

 widest leaves has the longest calyx lobes. The plants are more or less 

 pubescent and an extreme form which is densely pubescent all over is f. 

 pubescens (Britt.) Fern. (Rhodora 38: 444. 1936.) I have the form from 

 Perry and Pike Counties. 



Md. to Iowa, southw. to Ala., Ga., and Ark. 



3. Houstonia angustifolia Michx. Narrowleaf Houstonia. Map 1908. 

 I found this species in very shallow soil on top of the high cliff of the Ohio 



