128 BICKNELL: FERNS AND FLOWERING PLANTS OF NANTUCKET 
R. roribaccus Rydb. 
This plant, as I understand it, although subject to much varia- 
tion, is stouter and more copiously armed throughout than 
either R. Baileyanus or R. procumbens, and has ascending early 
shoots which become long-trailing and much branched. It is 
further and especially characterized by 5-foliolate primary leaves, 
on strongly armed petioles, with large, coarsely and acutely doubly 
dentate or incised, thinly pubescent leaflets; the terminal one 
very broad, even broader than long and sometimes 9 cm. wide; 
the middle pair often on slender petiolules 5-10 mm. long; the in- 
florescence is a loose corymbiform raceme of 3-7 flowers, on elon- 
gated and erect pedicels becoming 6-8 cm. long; the pedicels are 
often copiously armed, frequently invested with gland-tipped 
hairs, and subtended by very large unifoliate often lobed leaves; 
the flowers are smaller than in R. Baileyanus, with narrower petals, 
the sepals often setulose and foliaceous. 
Met with at only two stations on Nantucket: dry sloping field 
southwest of Millbrook Swamp, June 9, 1908, not yet in flower, 
and along the railroad about the second mile, June 23, 1910, passing 
out of bloom. In specimens from both of these stations the 
inflorescence is less conspicuously leafy than certain forms col- 
lected on Long Island, in which the unifoliate leaves are some- 
times 6-8.5 cm. broad. 
* RusuS ENSLENII X PROCUMBENS. 
R. geophilus Bld., in part. 
Prostrate and long-trailing, often with elongated branches, the 
new shoots sometimes ascending; stems slender, terete, soft, 
weakly armed with very small scattered prickles or almost un- 
armed; prickles very short, rather broad-based, mostly retrorse or 
décurved; primary leaves 5-foliolate or some 3-foliolate, on slender, 
thinly pubescent, sparsely armed petioles 3-5 cm. long; leaflets 
rather thin, dark green and sparsely appressed-pubescent on the 
upper surface, paler and minutely subappressed-pubescent to 
glabrate beneath, acutely serrate to dentate-serrate, often with 
irregularly cut teeth; odd leaflet rhombic-ovate to ovate-oblong, 
rounded or subcordate to subcuneate at base, on a stalk 0.5-2 cm. 
long, attenuate or acuminate at apex, sometimes cleft below to 
form two basal lobes, or not seldom parted bilaterally into a dis- 
tinct pair of accessory leaflets, making the leaf quasi-pinnate and 
