Classification of Echinocereus triglochidiatus
and Geographical Ranges of its Varieties - Answer Key
Assignment: (20 points)
(1) Read the attached table from a book called "Cacti of the United States and Canada" written and published in 1982 by Lyman Benson. Government agencies and many botanists refer to this book for the taxonomy of this species of cactus.
Cactus Anatomy: In order to read and understand what the literature
says about the descriptions and classification of cacti, an understanding of
the general anatomy of a cactus is helpful. Refer to the following diagram to
identify each of the following structures: stem, ribs, areoles, spines (central
and radial)
(2) Study the the distributions of each of the four varieties of E. triglochidiatus and draw in the ranges of each of the varieties on the map provided, using a different colored pencil for each variety, and making a legend in the lower left-hand corner of the map to indicate which variety is represented by which color. (7 points)
See attached map.
(3) Study the descriptions of the stem, rib and spine characteristics to determine what characteristics are definitive of the arizonicus and neomexicanus varieties. Make a list of the characteristics of each of these two varieties. (7 points)
|
Characteristics |
var. arizonicus |
var. neomexicanus |
|
# of stems |
few stems |
5-45 stems |
|
stem size |
to 40 cm long |
20-30 cm long |
|
# of stem ribs |
±10 ribs |
8-12 ribs (mostly 10) |
|
spine color |
dark gray spines |
tan or pink spines, becoming gray |
|
spine length |
to 3.8 cm long |
to 3.8 cm long |
|
central spines |
1-3 gray or pinkish central spines |
2-4 gray central spines |
|
radial spines |
5-11 radial spines, shorter than |
9-12 radial spines, half as long as |
|
# of central spines |
1-3 central spines |
2-4 central spines |
|
stem diameter |
stem diameter 7.5-10 cm |
stem diameter 7.5-10 cm |
(4) Formulate a Hypothesis: Based on the slide photographs of each variety, the geographical ranges and the descriptions of the characteristics of each variety of cactus, do you think that arizonicus is a distinct variety? Or, do you think that populations in SE Arizona (called var. neomexicanus) could also be arizonicus? State your hypothesis below and give a reason/rationale for your opinion. (6 points)