Vines and Climbing Plants of Puerto Rico and the Virgin Islands

Vines and Climbing Plants of Puerto Rico and the Virgin Islands 13
the terminal leaflet of the leaves (Fig. 4E). They
are simple, trifurcate, or sometimes are found to
be modified into a harpidium or small claw or
into small adventitious discs.
E. Tendrils derived from the leaf sheath. In the
Smilacaceae (Fig. 4F), the tendrils represent a
prolongation of the leaf sheath.
2. Twining plants (Fig. 4G). Twining plants,
commonly called vines, have active mechanisms
to climb on and attach themselves to the host
plant. They present a circumnutational movement
in which their stems, somewhat arching in the
distal portion, rotate on their own axis, rather like
the hands of a clock. This movement is essential
so that the vine can locate a structure on which it
can climb and thus use as a source of support.
The principal shoot of a vine rotates freely until
it runs into some structure that presents enough
resistance. Once this has happened, the stem of
the vine continues its rotational motion, but in a
smaller spiral, thus twining around the host plant.
The greater the diameter of the host structure, the
more difficult is the ascent, because the vine’s stem
is subject to the force of gravity. Trees of excessive
diameter represent an obstacle for the vine’s
ascent.
3. Sensitive branches or leaves. This category is
analogous to tendrils, but does not present any
type of modification; in this case the branches or
leaves are sensitive (prehensile or twining)
without having any kind of structural
modification. This mechanism can be considered
to be active both in the task of climbing and in
that of attachment to the host plant. Examples of
species with sensitive stems are found in the
family Celastraceae, and species with sensitive
leaves are found in the genus Clematis (Fig. 4H)
of the family Ranunculaceae.
4. Adventitious roots. Adventitious roots do not
really represent an active climbing mechanism
except in young plants, but in adult plants they
are very effective in the task of holding onto the
host plant. Examples are found in the genus
Marcgravia of the family Marcgraviaceae and the
genus Schlegelia of the family Schlegeliaceae.
5. Cauline or foliar spines. The presence of
spines on the stems or leaves of some climbing
species may be considered to be an active
mechanism for holding onto the host plant but
not necessarily for the task of climbing. Examples
of these structures are found in the cacti, some
species of the genera Mimosa and Acacia of the
family Fabaceae, the genus Celtis of the family
Ulmaceae, and the genus Berylsimpsonia of the
family Asteraceae.
6. Clambering plants. Clambering plants are
climbing plants that manage to climb on and gain
support from other plants by means of passive
mechanisms, that is, leaning against and growing
upon the host plant. Examples of this type of plant
are found in the genus Lepidaploa of the
Asteraceae and the genus Senna of the Fabaceae.
DIVERSITY AND DISTRIBUTION
The total number of species of climbing plants
that are found in Puerto Rico and the Virgin
Islands amounts to 386, distributed in 64 families
and 187 genera. Of these, 274 are native, 34 are
endemic, 64 are naturalized, and about 49 are
commonly cultivated in our gardens. Among the
endemic vines is Neorudolphia, the only plant
genus endemic to Puerto Rico.
The naturalized species are usually tropical
weeds with a very wide distributional range, not
only in Puerto Rico and the Virgin Islands but
throughout the tropics. These species are generally
of rapid growth and are typically found in areas
of disturbed vegetation, such as abandoned farms,
roadsides, pastures, or secondary forests and
thickets. Examples of these species are: Asystasia
gangetica, Thunbergia alata, Thunbergia
fragrans, Cryptostegia grandiflora, Momordica
charantia, Lablab purpureus, Pueraria
phaseoloides, Vigna hosei, and Jasminum
fluminense.
The native species, as a general rule,
have a less widespread distributional range than
the naturalized species. The range varies from
species with a widespread neotropical distribution
to species that are restricted to a group of islands.
Similarly, within Puerto Rico and the Virgin
Islands these species can have quite a widespread
range or may be restricted to particular
ecosystems. Species with a widespread neotropical