islayensis is a small
cylindrical cactus with very woolly areoles and dark spreading
spines, it is indeed very
variable and has received many names, but it is clear from fieldworks
that the different wild populations constitute a single but multiform
species. The var. lindleyi has fewer spines, the
var. lindleyi "paucispina" is very similar to
lindleyi (if not the same) but usually has stronger spines.
Stems: Grey-green, 5 to 40 cm
tall (or more long), 5 to 20 cm in diameter.
Ribs: 19 to 25 low and obtuse.
Areoles: Approximate, very
woolly, with grey-brown felt
Spines: Variable in colour, horn-coloured, brow to shiny black,
turning grey as they age.
Central spines: 4 to 7 spreading, thick, 12-16 mm long.
Radial spines: 12 to 22, shorter, radiating, (1-)6-10 mm long.
Flowers: Diurnal, 1,5 - 4 cm long and in diameter, born on
younger areoles from a yellowish
woolly crown in summer, wide
funnelform, yellow, outer perianth segments often reddish, floral tube
short with tufts of dense wool and long reddish bristles.
Fruits: Characteristic, up to 5 cm long, club shaped,
balloon-like, pinkish to red, openings at maturity by basal pores.
Pericarp initially fleshy but the interior always dry when mature.
Seeds: Broadly oval.