Greek gymnos — naked, kalyx—bud.

Body solitary or in clusters, spherical or compressed spherical. Ribs 4-15 or more, sometimes in spirals, tuberculate, spiny. Flowers diurnal, usually arising near the tip, funnel- or bell-shaped, white or pink, occasionally red or yellow; stamens often in 2 groups, one around the style immediately above the nectar chamber, the other towards the flower throat. Pericarpel and tube with broad, blunt scales which have characteristic transparent edges, the axils without hairs or spines. Fruit from round to oblong or widest at one end, dry or juicy.

Seeds are technically important in distinguishing species and species groups but are avoided here to simplify the account.

Seed, occasionally by cuttings or offsets.

Tubercles with a chin-like swelling below the areoles; scales on ovary and flower tube broad; flowers and fruits without hairs, bristles or spines.

Probably about 50 species from S America (Argentina, Bolivia, Brazil, Paraguay and Uruguay).

 

FLOWERS RED

G. baldianum (Speg.) Speg., Crimson Star from NW Argentina has 9-11 ribs without central spines and 3-7 radial spines to over 1 cm long. Flower colour variable but often crimson.

 

PALE-FLOWERED SPECIES (PINK, ORANGE, LILAC, GREENISH) WITH PERIANTH SEGMENTS HAVING A DARK STRIPE

G. cardenasianum F.Ritter  See under description for species.

Also G. spegazzini Britton & Rose, G. bruchii (Speg.) Hosseus, G. mihanovichii (Fric & Gürke) Britton & Rose, G. horstii Buining and G. mihanovichii.

 

PALE-FLOWERED (PINK, ORANGE, LILAC), PERIANTH SEGMENTS WITHOUT A STRIPE

G. saglionis (Cels) Britton & Rose See under description for species.

Also G. bueneckeri Swales and G. multiflorum (Hook.) Britton & Rose from N Argentina has bell-shaped not funnel-shaped flowers.

 

FLOWERS WHITE WITH RED THROAT

G. quehlianum (Haage) A. Berger See under description for species.

Also G. fleischerianum Backeb. and G. vatteri Buining.

 

FLOWERS WHITE (OCCASIONALLY TINGED PINK)

G. denudatum (Link & Otto) Pfeiff. See under description for species.

Also G. anisitsii (K. Schum.) Britton & Rose [G. damsii (K. Schum.) Britton & Rose], G. platense (Speg.) Britton & Rose, G. gibbosum (Haw.) Pfeiff., G. schickendantzii (A. Weber) Britton & Rose and G. marsoneri (Fric) Ito.

Source: Thompson, A, ; Forbes, S.; Spencer, R. (1997). Cactaceae. In: Spencer, R.. Horticultural Flora of South-eastern Australia. Volume 2. Flowering plants. Dicotyledons. Part 1. The identification of garden and cultivated plants. University of New South Wales Press.