Aylostera nigricans (Wessner) Mosti & Papini
Mosti & Papini (2011) recognise two subspecies of Aylostera nigricans: the nominate, and A. nigricans ssp. albispina (Rausch) Mosti & Papini. The nominate has bronze spines and intense red flowers; A. n. albispina has white spines and deep ruby red flowers. Both have dark green shoots when new, turning to brown with a purplish sheen, which is where the name comes from. Plants with paler flowers are sometimes found (e.g. RH500 below). These are sometimes listed as A. pygmaea.
Note that the former A. nigricans var. carmeniana is now given specific status as A. carmeniana (Rausch) Mosti & Papini.
The descriptions for both subspecies are here.
Plants of this species in the collection include:
Aylostera nigricans JO190
Aylostera nigricans MN82
Aylostera nigricans MN117
Aylostera nigricans WR14