The distribution of this bramble is centred on the county of Berkshire, from which its species name derives, and extends west to south Wales and east to Essex and Kent. In Hampshire it seems to be particularly associated with alder woods, but is also found in other types of woodland and on heathland. It can be distinguished by the combination of narrow white petals, broadly elliptical terminal leaflet and the glandular, but hairless stem with numerous fine, curved prickles.
The stamens are a little longer than the styles, which are tinged reddish at the base. This colouration is just about visible in these photos of flowers in deep shade, but can be much more obvious. In my local population 6 and 8-petalled flowers seem to be common and help give the flowers a distinctive look.
The sepals and all the floral branches are strongly glandular – more obvious in the open-grown specimen below. The sepals point outwards during flowering, forming a star-like cradle around the developing fruit. Note also that some of the sepals have leafy appendages.
Stems are prostrate or low-arching but the species often forms pure patches up to about a metre in height. Colonies can be very extensive.
Leaves are relatively large (the terminal leaflet typically around 10cm long) and thin when growing in deep shade. As with all brambles, the leaves become thicker and more strongly textured when growing in full sun and can then look completely different (compare the two photos below).
The leaf underside is hairy but not felted. The hairs on the veins are pectinately arranged.
The stem ranges from almost round in cross-section to bluntly angled, typically green in the shade but becoming yellowish- or reddish-brown in the sun. The longest prickles are mainly confined to the angles, but there are also many smaller pricklets and acicles on the faces, of varying sizes. The glands mainly occur on the ends of these. This very prickly appearance is typical of brambles in the Hystrices.
A stem growing in full sun. A distinctive feature of this species is the colouration of the prickles which are yellowish at the base and tip, but red in the middle.