Vines and Climbing Plants of Puerto Rico and the Virgin Islands

Vines and Climbing Plants of Puerto Rico and the Virgin Islands 11
cylinders of different diameters. This pattern is
visible only in mature stems. Examples are found
in the genus Chiococca (Fig. 2C) of the family
Rubiaceae and in the genus Turbina (Fig. 2D) of
the family Convolvulaceae.
4. Compressed stems. This pattern, with the
vascular cylinder in a central position, is obtained
through asymmetrical secondary growth, in which
the stem grows laterally in two opposing
directions. Examples of this pattern are found in
the genera Rhynchosia (Fig. 2E) and Dioclea of
the family Fabaceae.
5. Deeply lobed stems. This pattern is achieved
by secondary growth of the stem in particular
regions, giving rise to the lobes. Examples of this
pattern are found in the genus Marcgravia (Fig.
2F) of the family Marcgraviaceae, in the genus
Distictis (Fig. 3A) of the family Bignoniaceae,
and in the genus Passiflora (Fig. 3F) of the family
Passifloraceae.
6. Stems with the xylem forming a cross of 4-
12 arms. This pattern is produced through
differential secondary growth of the xylem and
phloem, with the result that there is more xylem
tissue in the area of the arms. This pattern is very
common in climbers of the family Bignoniaceae,
e.g., Arrabidaea, Cydista (Fig. 3B) and
Amphilophium (Fig. 3C).
7. Cylindrical stems with lobed xylem. These
are formed by the pronounced growth of xylem
tissue in certain regions of the stem. This pattern
can be seen in the genus Passiflora of the family
Passifloraceae. In the genus Macfadyena (Fig. 3D)
of the family Bignoniaceae, this pattern is
obtained through differential growth of the xylem
and phloem, producing more xylem in the area
of the lobes.
8. Cylindrical stems with conspicuous rays. A
cross section of the stem shows the presence of
wide parenchymatous rays inserted in the xylem
tissue. Examples of this pattern can be seen in
the genera Pristimera (Fig. 3E) and Hippocratea
of the family Celastraceae and in the genus
Psiguria of the family Cucurbitaceae.
CLIMBING AND ATTACHMENT
MECHANISMS
Climbing plants achieve their objective of
climbing on and attaching themselves to host
plants by means of different active or passive
mechanisms. Some species have active
mechanisms for both tasks, while others are
passive in one or both of them. Twining plants,
as well as those that have tendrils or sensitive
stems, possess active mechanisms that permit
them to achieve both objectives. Climbers with
recurved spines or adventitious roots do not have
active climbing mechanisms, but these structures
represent an active mechanism for the task of
attaching them to the host plant. Clambering
plants represent an extreme case in which both
mechanisms are passive. The different climbing
and attachment mechanisms are listed and
discussed below.
1. Tendrils. Tendrils are sensitive, usually
filamentous appendages with which some plants
climb on and attach themselves to host plants.
These are developed from various structures of
the plant body, and are discussed below under the
following categories.
A. Axillary tendrils. These are homologous to
short axillary branches; examples are found in
the Cucurbitaceae (Fig. 4A) and Passifloraceae.
In the genus Gouania (Rhamnaceae) they may
develop at the end of a short axillary branch,
which sometimes produces a single leaf (Fig. 4B).
B. Tendrils opposite the leaves. This type of
tendril is probably homologous to the distal end
of the main stem of the plant; consequently, the
branches form a sympodial system. Examples of
this type are found in the Vitaceae (Fig. 4C).
C. Tendrils in the inflorescence. In the climbing
Sapindaceae, the tendrils are homologous to the
basal lateral branches of the inflorescences. They
are present in pairs in the basal flowering portion
of the inflorescence. Examples of this type are
found in the genera Paullinia and Serjania (Fig.
4D).
D. Foliar tendrils. In many climbing genera of
Bignoniaceae, the tendrils are found to replace