Classification of Echinocereus triglochidiatus
and Geographical Ranges of its Varieties
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)
(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 |
___________________
|
___________________
|
|
stem size |
___________________
|
___________________
|
|
# of stem ribs |
___________________
|
___________________
|
|
spine color |
___________________
|
___________________
|
|
spine length |
___________________
|
___________________
|
|
central spines |
___________________
|
___________________
|
|
radial spines |
___________________
|
___________________
|
|
# of central spines |
___________________
|
___________________
|
|
stem diameter |
___________________
|
___________________
|
(4) Formulate a Hypothesis: Based on the digitized 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)