15 
VI. 
CENTAUREA CALCITRAPA, Linn£. 
The Star-Thistle. 
The specific name has been chosen in allusion to the very 
spinular flower-headlets, its etymology being derived from the 
Latin name of an ancient contrivance to impede the progress of 
horsemen in warfare. The British vernacular has been in use 
since medieval times. Indigenous from Middle Europe to 
Western Asia and Northern Africa. 
Flowering under ordinary circumstances only once from 
the same root. Neither tall nor robust, often much spreading 
and very branched, imperfectly beset with short hairlets, only 
occasionally reaching a height of 3 feet. Leaves rather small, 
unless those near the root, always lax, simply sessible, pinnati- 
lobed or the upper gradually undivided, the basal leaves some- 
times doubly dissected, the lobes and undivided portion always 
narrow and distantly or imperfectly denticulated. Headlets of 
flowers singly terminal and lateral, almost sessile. Involucral 
bracts glabrous, at their lower portions closely appressed, dilated, 
pale, uniting into an almost conic-ovate form, the upper ending in a 
spreading comparatively long and strong spinule, excepting the 
innermost bracts ; the spinule towards its base denticulate- 
spinular and somewhat channelled. Receptacle beset with 
numerous capillulary-setular white bracts. Flowers of nearly 
the same length, not very numerous, the outermost generally 
sterile. Corolla purplish in the majority of the plants, its tube 
very thin, widened towards the summit, the five lobes narrow; 
corolla of the circumferential flowers longer lobed. Stamens 
irritable, alternate to the corolla-lobes, their filaments beset with 
very minute papillular hairlets ; anthers reddish, connate, linear - 
sagittate. Style capillulary, bearing papillular hairlets at the 
upper end ; stigmas narrowly semicylindrie, coherent except at 
the top. Ripe fruit glabrous, cuneate-ellipsoid, somewhat com- 
pressed, slightly biangular, at the base unilaterally impressed or 
almost excised, outside pale with darker striolate spots (the 
lithographic colouration on the plate incorrect). Pappus absent. 
A very closely allied plant, showing a transit to Centaurea 
Iberica (Stephan), differs chiefly in having a short pappus, at all 
events to the fruits of the marginal flowers. A variety, here 
also already immigrated, in which the lower involucral bracts are 
terminated only in very short spinules, approaches Centaurea 
Pamphylica (Boissier and Heldreich). 
Explanation of Plate VI. 
Flowering branch with its leaves, natural size. 
1. Longitudinal section of a headlet of flowers, slightly 
enlarged. 
2. A separate corolla, showing also style and stigmas. 
