1a.

Flowers with pericarpel covered by flakes and hair.
Habitat: coastal hills Region Antofagasta

2

1b.

Flowers with bare pericarpel and floral tube.
Habitat: Coastal hills of the mountain ranges N. of Antofagasta and S. of 31^o Lat. S.

4

2a.

Solitary plants or forming cushions on the surface of the ground, with stems of more than 4 cm diameter, very marked ribs and long and thick spines.

3

2b.

Stem simple or sparsely offsetting, 2 to 4 cm. diameter, black-green, hard. Ribs, none; tubercles arranged in spirals. Spines, 8 to 14, curved, fine, 3 to 6 mm. long.
Habitat: Plains around El Cobre, Region Antofagasta

C. TENUISSIMA

3a.

Plants semi arbustivas, generally simple; stem moderately hard, 6 to 8 cm. in diameter. Root: tap root, connected to the stem by means of a narrow neck.
Habitat: Hills near Tocopilla

C. TOCOPILLANA

3b.

Plants arbustivas, hard stems that offset profusely forming cushions of 1 to 2 m.; each head 8 to 12 cm. in diameter. Grey-greenish epidermis. Root fasciculate and fibrous. Big areoles, more than 1 cm. Spines 1.6 to 6 cm long, strong and stiff, straight or curved. Recovered pericarpel with some flakes, abundant hair and wool.
Habitat: Hills around El Cobre, Region Antofagasta.

C. SOLARIS

4a.

Roots: without tap root; roots fibrous fasciculate         

5

4b.

Roots: with augmented tap roots present      

9

5a.

Stem simple, offsetting or forming cushions. Epidermis white or pale grey, powdered with a waxy layer. Spines variable in number, long, colour and texture 

6

5b.

Simple stems or with 2 to 3 branches; 7 to 18 cm. in diameter. Green or brown epidermis, without wax layer. Radial spines, 7 at 9, to 2 cm. long; central spines, 3, 1 to 3 cm. long.
Habitat: Coastal, Region Atacama

C. ECHINOIDES

6a.

Plants with simple stem or some tendency to ramify

7

6b.

Plants always offsetting to form cushions 1 to 2 m in diameter

8

7a.

Spines, 20 to 30 per areole, white or clear in colour, soft, long and flexible, covering the apex. 
Habitat: High hills to the north of Taltal, Region Antofagasta 

C. KRAINZIANA

7b.

Spines, 0 to 12 per areole, dark, straight, strong, lasting. Apex densely and profoundly woolly, white to brown in colour.
Habitat: Taltal, Region Antofagasta

C. CINEREA

8a.

Ribs, 15 to 21. You prick with spines strong of red tone to black, 4 to 7 for areole, of 1 to 3 cm. of long. Spiny covered apex with orange down.
Habitat: Esmeralda, Region Antofagasta 

C. LONGISTAMINEA

8b.

Ribs, 21 to 33. Spines long and thin, 2 to 5 cm. long. Spiny apex with scarce and superficial layer of whitish wool.
Habitat: Carrizal Bajo, Region Atacama

C. DEALBATA

9a.

Root connected pivotante to the stem directly, without neck        

10

9b.

Root connected pivotante to the stem by means of a narrow neck           

11

10a.

Stem with greyish epidermis      

12

10b.

Stem with green epidermis        

13

11a.

Stem with greenish-grey to black epidermis

14

11b.

Stem with green or brown epidermis

13

12a.

Plants with simple, offsetting stem or forming cushions of up to 1 m.; individual heads 6 to 15 cm. in diameter. Ribs, 9-14. Radial spines, 5 to 8; central spines, 1 to 4, yellow to black, strong, hard, straight.
Habitat: From Antofagasta, II Region, to Caldera, III Region.

C. ATACAMENSIS

12b.

Plants tend to form cushions of up to 1 m., with heads of 8 to 15 cm. in diameter. Ribs, 15 to 20. Radial spines, 7 to 9; central spines, 1 to 4, 1 to 2 cm. long, white to brown, straight, strong.
Habitat: N. of Chañaral, Region Atacama

C. CINERASCENS

13a.

Plants tend to form cushions of 0.6 x 1 m.; individual heads 7 to 10 cm. in diameter, greenish grey to brown in colour, hard, apex with spines and hair. Ribs, 18 to 33. Spines, 6 to 10 per areole, all 5 cm. long, brown in colour, aciculate, straight. Areoles 0.5 to 1 cm. apart and recovered with scarce yellowish down.
Habitat: N. of Chañaral, Region Atacama

C. SERPENTISULCATA

13b.

Solitary stems or tending to form cushions; individual heads of 7 to 10 cm. in diameter, hard, with apex covered with abundant felt. Ribs, 10 to 14. Spines, 5 to 9 per areole, 2 to 5 cm. long, dark. Areoles almost joined to each other and with abundant wool.
Habitat: Caldera, Region Atacama

C. MARGINATA

14a.

Apex of the stem level or below the surface

15

14b.

Apex generally on the surface of the floor

16

15a.

Stem simple or sparsely offsetting, 3 to 6 cm. diameter, grey-greenish or coffee-reddish, relatively soft. Ribs, 10 to 14, not very apparent and almost completely dissolved in tubercles. Spines, 0 to 4, 2 to 4 mm. long, fine, straight. Flowers with almost completely naked floral tube.
Habitat: Hills around Chañaral, Region Atacama 
 

C. HYPOGAEA

15b.

Stem simple or sparsely offsetting, of 2 to 4 cm. of diameter, black-green, hard. Ribs, 0; tubercles arranged in spirals. Spines, 8 to 14, 3 to 6 mm. long, curved. Flowers with some down in the tube.  
Habitat: Plains around El Cobre, Region Antofagasta

C. TENUISSIMA

16a.

Stem generally simple or with few offsets (not more than 3), flat, level with ground, or globular

17

16b.

Generally offsetting stems

18

17a.

Stem simple, of green epidermis, moderately hard 

19

17b.

Stem brown, hard, simple or sparsely offsetting, spherical, of 5 to 8 cm. of diameter. Spines brown, 8 to 10 per areole, 1 to 2.5 cm. long, acicular.
Habitat: Mountains of Copiapó, Atacama

C. MEGARHIZA

18a.

Stems soft or moderately hard  

20

18b.

Stems hard, forming dense cushions of 50-70 cm., with individual heads 6 to 10 cm. Ribs, 10 to 15. Spines strong, 2 to 5 cm. long; radial spines, 7 to 12; central spines, 2 to 6. Yellow or red flowers.
Habitat: Desert area to the S. of Taltal, Region Antofagasta

C. DESERTORUM

19a.

Sculptured from 6 to 8 cm. in diameter, grey-green. Ribs, 10 to 14, not very remarkable in the young plants. Spines covering the stem: radial spines, 10 to 12; central spines, 1 to 4. Flowers with some wool around the tube.
Habitat High hills near Tocopilla, Region Antofagasta
 

C. TOCOPILLANA  

19b.

Stems from 8 to 10 cm. diameter, grass green. Well-defined ribs, 12 to 13. Spines acicular, straight, not covering the stem: radial spines, 6 to 10; central spines, 1 at 7. Flowers bare.
Habitat: Chañaral, Region Atacama       

C. CHANARALENSIS

20a.

Offsetting stems forming not very dense cushions, of spherical or elongated heads, 3 to 9 cm. diameter. Ribs, 8 to 14, poorly defined and dissolved in tubercles. Spines, 1 to 15 per areole, fine. Flowers yellow.
Habitat: Humid belt around Paposo, Antofagasta  

C. HUMILIS

20b.

Stems usually profusely offsetting and forming dense cushions; heads quite variable individual in size. Ribs, 13 at 18, pronounced or not very defined, with big tubers. Spines very variable: radial spines, 5 to 7; central spines, 0 to 1. Flowers yellow, with tepals reddish on the outside.
Habitat: Coastal and mountains of the Regions III and IV

C. COQUIMBANA