Dichotomous Key/Ceratozamia

Ceratozamia is a genus of New World cycads in the family Zamiaceae. The genus contains 27 known currently living species and one or two fossil species. Most species are endemic to mountainous areas of Mexico, while few species extend into the mountains of Guatemala, Honduras and Belize. The genus name comes from the Greek ceras, meaning horn, which refers to the paired, spreading horny projections on the male and female sporophylls of all species.

Many species have extremely limited ranges, and almost all described species are listed as vulnerable, endangered, or critically endangered by the IUCN Red List. The whole genus is listed under CITES Appendix I / EU Annex A, and CITES prohibits international trade in specimens of these species except when the purpose of the import is not commercial, for instance for scientific research. Illegal plant poaching has posed a major threat to Ceratozamia species.

This is the key to the Ceratozamia:

Start

 * 1: Leaflets are the widest above the middle of the frond.
 * 2: Leaflets are the widest below the middle of the frond.

1
Leaflets are the widest above the middle of the frond.
 * 3: Leaflets are evenly spaced.
 * Ceratozamia hildae: Leaflets are clustered along the rachis.

2
Leaflets are the widest below the middle of the frond.
 * 9: Leaflets are less than ten millimeters wide.
 * 10: Leaflets are greater than one centimeter wide.

3
Leaflets are evenly spaced.
 * 4: Leaflets are less than five centimeters wide.
 * 5: Leaflets are more than five centimeters wide.

4
Leaflets are less than five centimeters wide.
 * 6: Leaflets are leathery; stiff and tough, but somewhat flexible.
 * 7: Leaflets are not leathery.

5
Leaflets are more than five centimeters wide.
 * Ceratozamia euryphyllidia: Leaflets are nine centimeters wide or greater, and translucent.
 * 8: Leaflets are less than nine centimeters wide, and not translucent.

6
Leaflets are leathery; stiff and tough, but somewhat flexible.
 * Ceratozamia microstrobila: Leaflets are three centimeters wide or less.
 * Ceratozamia zoquensis: Leaflets are three centimeters wide or greater.

7
Leaflets are not leathery.
 * Ceratozamia morettii: Leaflets curve upwardly, similar to the blade of a scythe.
 * Ceratozamia latifolia: Leaflets do not curve upwardly.

8
Leaflets are less than nine centimeters wide, and thin or papery.
 * Ceratozamia zoquensis: Leaflets are leathery; stiff and tough, but somewhat flexible.
 * Ceratozamia miqueliana: Leaflets are not leathery.

9
Leaflets are less than ten millimeters wide.
 * Ceratozamia norstogii: Rachis is straight.
 * 11: Rachis is not straight; usually twisted or contorted.

10
Leaflets are greater than one centimeter wide.
 * 12: Leaflets are ten to fifteen millimeters wide.
 * 13: Leaflets are two to five centimeters wide.

11
Rachis is not straight.
 * Ceratozamia mirandai: Petiole and rachis have stiff prickles.
 * Ceratozamia zaragozae: Petiole and rachis lack prickles.

12
Leaflets are ten to fifteen millimeters wide.
 * 14: Petiole and rachis are green, bearing stiff prickles.
 * Ceratozamia kuesteriana: Petiole and rachis are dark green to brown, lacking stiff prickles.

13
Leaflets are two to five centimeters wide.
 * 15: Leaflets are three centimeters wide or greater.
 * Ceratozamia mexicana: Leaflets are three centimeters wide or less.

14
Petiole and rachis are green, bearing stiff prickles.
 * 16: Rachis has stiff prickles or spines.
 * Ceratozamia matudae: Rachis lacks prickles or spines.

15
Leaflets are three centimeters wide or greater.
 * Ceratozamia robusta: Petioles have many stout prickles or spines.
 * Ceratozamia whitelockiana: Petioles have fewer small prickles or spines.

16
Rachis has stiff prickles or spines.
 * Ceratozamia alvarezii: Leaflets are ten millimeters wide or less.
 * Ceratozamia sabatoi: Leaflets are ten millimeters wide or greater.