All plants are related to each other in the sense that every one of them
is descended from a common primitive uni-cellular life form which came
into existence on this planet millions of years ago. As the remote
progeny of that ancestral cell, or group of cells, became scattered over
the earth and faced diverse conditions, which in turn changed with the
ages, these millions of related organisms exhibited profound changes
such that the differences in form, size and structure have become more
noticeable than are the badges of common inheritance. This is the
process called Evolution. Changes are established so slowly, however,
that the immediate descendants of any particular plant, or the offspring
from cross-pollination within a closely related group, will continue for
many generations to be substantially identical in structure with the
parents. As long as substantial identity in structure exists, all of
these individual plants form a single “species.” As these species are
discovered, botanists give each of them a Latin name. Within Colorado
over 2000 such separate species of flowering plants are known. Minute
variations such as color of petals or degree of hairiness of leaf or
stem are treated as “varieties” within the species.
Many thousands of these substantially identical plants may be found
scattered over parts of a state, or over several states, or even
throughout a life zone area comprising parts of several continents.
Within the life zone favorable to them, the only geographical limits
seem to be those affecting distribution of live seed.
In the search for plants, many different species are found, either in
the same or more often in different localities, in which the
resemblances are close; in fact many parts are almost identical, but
persistent differences are also present. A common ancestor several
hundred or several thousand years back may have existed, but
evolutionary changes have brought noticeable differences in the
respective descendant groups. If the changes are not too great,
especially if the mechanisms of reproduction have not been so greatly
changed as to make cross-pollination totally impossible between plants
of the several species, these related species, wherever they may have
been found, are said to comprise a “genus.” To this, also, a Latin name
is given. _Lillium_, for example, is the generic name of all true lilies
everywhere; _umbellatum_, however, is the specific name of the group to
which our Colorado mountain lily belongs; and “_Lillium umbellatum_” is
the full name of the plant shown on page 10.
Still greater differences in plant and flower structure are found,
coupled, however, with strong resemblances in significant parts of the
structure. This has led to grouping a considerable number of genera
together into a “family.” Latin names also are given to the families.
For these names there are, in most cases, well established English
equivalents which we have used here without repeating the more technical
family name. Within each family all genera and each species of every
genus will exhibit strong resemblances in the mechanism of seed
production, and the general pattern of the organs of reproduction will
be recognizably similar. For example, all species in the rose family
(with very few exceptions) have numerous stamens arranged in whorls;
they also have a calyx formed of five sepals joined together at the
base.
Other groupings, such as “Orders” comprised of several families, or
“tribes” composed of several genera within a family, are used by
botanists, but for the purposes of this booklet we have used only the
names of families, genera and species.
To the amateur one of the most interesting phases of plant
classification is the way in which, as we pass from one life zone to
another, or from one part of the state to another part within the same
life zone, we find that a plant species which we have observed at one
spot, is replaced, at another, by a different species within the same
genus. We find our white mariposa, _Calochortus gunnisonii_, on the east
side of the mountains, then, in flat clay plains in southwestern
Colorado, we find the sego lily, Calochortus nuttallii, which is a
similar, but quite distinct mariposa with cream-colored petals and a
crooked, much shorter stem. Beyond the boundaries of Colorado numerous
other species of Calochortus are found, all of them different from ours,
but all of them quite obviously mariposas.