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.
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