I'OLYsriCHUM ACULEATDM. 233 
/ POLY'STICHUM ACULEAT UM. 
THIS lias been included by various botanists in the 
genera Aspidium and Polypodium, but all have retained 
the specific name aculeatum, prickly, on account of the 
sharp-pointed character of the teeth on the edge of the 
leafits. Some botanists consider it and P. angulare 
only different forms of the same species. In English it 
is known as the Common Prickly Shield Fern. 
Root large, woody, enlarging very slowly, tufted, pro- 
ducing many coarse, wiry side rootlets. Fronds numerous, 
spreading in a circle; their upper side shining, dark 
bluish green, but paler underneath ; in general outline 
spear-head shaped, sometimes broad, at others narrow, 
but always tapering to a point, and rather stiff when 
mature, though very limp when young ; in height from 
two to three feet. Stemleafleted to within three or four 
inches of its base, and covered throughout with reddish- 
brown scales. Leaflets alternate, close together, narrow 
spear-head shaped, tapering to a point. Leafits all 
rather convex, alternate, the upper one next the stern 
always larger than the others, and parallel with it, 
giving the stem somewhat the appearance of being 
bordered with alternate leafits. They are distinctly, 
though rather shortly stalked, irregular arrow-head 
shaped. Towards the upper end of the leaflet they are 
joined together at their base (decurrent); the upper side 
of each is largest, sharply saw-toothed, the teeth being 
unequal, and the points so sharp as to b really prickles : 
