Common Trees of Puerto Rico and the Virgin Islands

When the plant family of a tree is not known,
this key to the families of the trees of Puerto
Rico and the Virgin Islands aids identification.
Eighty-eight plant families are included, all 75
with native trees and also 13 others with common
introduced trees. Of these, G8 families are represented
in this volume, 33 by a single species illustrated,
however. Additional keys to the remaining
218 of the 250 tree species are inserted in the
text under all 35 families with 2 or more species
illustrated. Howeve?, bhe related species compared
briefly and various genera of less common
trees not mentioned in the test are not keyed.
Some genera have been included in the key to
families also. If a plant family has only 1 or 2
genera of native trees, these generic names are
cited after the family name. Also, several genera
differing slight1 from the main characters of
7
their families lave been inserted separately.
However, this artificial key may not provide for
a few odd genera and extreme variations. Introduced
or exotic enera and families are indicated
by an asterisk (5.
Keys are outlines or shortcuts for identifying
trees or specimens by the process of elimination.
Thus, trees are divided into two groups according
to one or mom pairs of contrastin characters.
Eaoh group is divided successive f y into two
smaller groups until the name is reached. The
name of a particular s ecirnen is found through
4'
selection, one by one, o the group which fits and
by elimination of the others.
In these indented keys, paired grou s are designated
by the same letter, sinale an 2 double bepinning
with "A" and "AA?' at the left o$ the
page and are equally indented by steps. Th'e page
number refers to bhe descriptive text, the beginnin
of the family or genus listed. The 20
f
small amilies without page numbers are not men-
tioned further or represented among the common
trees described in this volume.
An unpublished card key to families of West
Indian trees by the senior author has served as the
basis for this one. Nontechnical characters and
those readily observed have been emphasized.
The descriptive terms are defined under the topic
"Explanation of Botanical Terms" (p. 9).
KEY TO FAMILIES
One character used in the key, presence or absence
of stipules (one or two scales at the base
of a leaf), may be difficult to determine because
the stipules sometimes are minute or shed early.
Stipules can be examined best in the bud and immature
leaves near the stem tip. Upon shedding,
tlie stipules leave a scar, ~vhich also may be minute.
Vegetative characters, especially those of leaves,
are placed first in the key. Some plant families of
trees can be recognized or identified by certain
combinations of vegetative characters alone. Homever,
many kinds of tropical trees have foliage of
similar appearance.
For positive identification of many families, the
reproductive characters of flowers, fruits, and
seeds are needed. Even when these are lacking,
old fruits may be located on dead branches or on
the ground, and one tree may be found flowering
out of season. Some stsrile specimens, those Iwking
flowers or fruits, can be identified to fmily
by the vegetative characters beginning the key.
If not, thekey will eliminate many families. Then
identification can be continued by consulting the
text and drawings for the remaining families.
The key to families is divided into four parts according
to the arrangement or position of the
leaves and the number of blades. Parts 1 and 2
are for tks a; th altarnate leuves, that is, attached
singly or 1 at u point on a twig (node). Parts
3 and 4 are for trees with opposite leaves, that is,
paired or 2 at a node, and also those with whorled
leaves, 3 or mom at a node. Parts 1 and 3 are for
trees with simple leaves, with 1 blade, and Parts
2 and 4, trees with compound leaves, divided into
3 or more blades (rarely only 2).
The first step in using this key to families is to
place the unknolvn tree or speciment in one of the
four groups listed below. Then continue the key
under the part or group on the page cited.
Part 1. Leaves alternate, simple (p. 22).
Part 2. Leaves alternate, compound (p. 25).
Part 3. Leaves opposite, simple (p. 26).
Part 4. Leaves opposite, compound (p. 27).