is characterized by polyphyllous sympodial growth with an elongate
shoot and no branches. After the shoot terminates in an inflorescence
or a series of inflorescences, a single branch arises from the lateral
bud, two nodes back from the apex (Madison, 1978). The stem branching
pattern as reported by Engler (1877) is as follows:
pattern depicted here is indefinitely repeatable, limited only by
change in the ecological conditions that allow flowering. (See also
section on GROWTH HABITS.)
may initially be only a few mm diameter in juvenile plants but up
to 6 cm diameter in adult plants. Syngonium stems probably
average 1 to 2 cm diameter. Stems are invariably green and presumably
photosynthetic in juvenile plants, but the epidermis soon loses
its color on adult plants (usually within 1 node below the inflorescence).
The possibility of having photosynthetic tissue in the creeping
phase of growth where internodes are elongate and leaves are small
(see section on GROWTH HABITS) would
be important ecologically.
general the stems of Syngonium are unbranched though branching
sometimes occurs, especially if the stem has been injured. Generally,
climbing stems have elongated internodes. The internodes are often
appreciably shorter on flowering portions than elsewhere. Some species,
especially those species with thicker stems, such as S.
crassifolium, S. schottianum
and S. sagittatum, may
have the internodes quite short on flowering segments.
segments are terete or more commonly oval in cross-section and have
a shallow groove on one side above the axillary bud. This generally
is diminished or absent distally. Birdsey (1955) reports a multiseriate
epidermis in Syngonium with the developing stem near the
apical meristem having only a single layer of cells and sections
distal to the apical meristem having 3 or more layers of epidermal
cells. Part of these layers may be suberized but at least the innermost
is not suberized. Birdsey (1955) reports that it is not yet known
whether this multilayered tissue arises from the epidermis or underlying
are to some extent flexible but, if bent, the outer epidermis often
cracks free. Even in undisturbed plants, the outer epidermis often
becomes cracked and peels. In such cases the outer epidermis is
generally brown or yellowish with the underlying epidermal cells
green or olive green. The color of the epidermis is sufficiently
variable to provide useful specific characteristics. For example,
the outer epidermis of S.
erythrophyllum always dries a characteristic brown only
a short distance from the stem apex. Drying plant collections invariably
causes shrinkage of the stem with the result that herbarium specimens
have the outer epidermis cracked or fissured and often peeled free
from the stem.
the case of S. angustatum
the epidermal cells are pushed out by underlying cells to provide
rough spots visible to the naked eye (Birdsey, 1955), while the
excrescences of S. podophyllum var. peliocladum are very
large, providing the chief taxonomic characters for its separation
from S. podophyllum var.
useful taxonomic character involving the stem is the presence or
absence of a waxy layer, although the character does not necessarily
maintain itself throughout the range of a species. For example,
the stems of S. podophyllum
in Mexico are glaucous and are useful there in separating it from
S. angustatum, but in Panama and in South America the stems
are never reported to be glaucous.
glaucous condition is also present on other parts, especially the
peduncle and the fruits, e.g., in
S. chiapense and S. macrophyllum. The glaucous peduncles
of S. angustatum are useful in separating it from S. podophyllum.
anatomy was dealt with briefly by Van Tieghem (1867) and will be
dealt with more completely in work underway by R. Keating of Southern
Illinois University, Edwardsville. Birdsey (1955) also presents
a thorough survey of stem anatomy.
Stem cross-sections of Syngonium show a well-defined layer
of collenchyma (cortex) beneath the epidermal layers with a poorly
defined boundary lacking between the cortex and the central vasculated
region of the axis (Birdsey, 1955). Starch grains are randomly distributed
throughout the parenchyma of both the central cylinder and the cortex,
and idioblasts containing raphides as well as cells containing druses
are present, though in lower frequency than in the petioles (Birdsey,
1955). The stem of Syngonium lacks a well-defined pith and
has the scattered vascular bundles characteristic of monocots. Always
present in the stems of Syngonium are articulated laticiferous
cells, i.e., secretory cells, which are placed end-to-end, forming
a continuous tube with numerous branches and anastomoses (Birdsey,
1955). The contents of the cells are rich in tannins as well as
latex (Solereder & Meyer, 1928).
roots of two types emerge just below each node of the stem. In addition
to a number of skototropic clasping roots, whose main function is
holding the plant to its support, there is a single feeding root
that is positively geotropic and diverges from the stem at an angle
that puts it into a position to absorb nutrients some distance from
the plant (Birdsey, 1955). The anatomy of these roots differ at
least quantitatively (Birdsey, 1955), with the feeding root having
greater overall diameter, a proportionally larger central cylinder,
and proportionally larger vessels.
phyllotaxy is reported as 2 2/5 divergence (Engler, 1877), though
the arrangement may be obscured by the slight twisting of the petioles
petiole of Syngonium is always conspicuously sheathed from
about the middle to near the apex, generally between the middle
and the upper 4/5 of the petiole. The sheath functions in protecting
the newly emergent leaves and the inflorescences. The sheath is
generally very broad, especially at the base, and the two sides
are generally quite unequal in height. The apical portion of the
sheath is often free-ending, and the free part varies from acute
to rounded or emarginate at the apex. The petiole of section Oblongatum
differs in being proportionately broader and extends often beyond
the base of the blade. The
petioles have a uniseriate epidermis, with numerous intercellular
spaces (Birdsey, 1955). The vascular bundles are irregularly scattered
throughout the fundamental tissues. Perhaps owing to the numerous
intercellular lacunae, the petioles of Syngonium are soft
and can be easily crushed in comparison to other aroid genera such
as Anthurium. The cross-sectional shape of the free portion of the
petiole beneath the blade often has taxonomic significance. Although
all are characterized by being rounded on the abaxial side and most
have a single more or less conspicuous adaxial rib, the rib varies
from being almost absent in the case of S.
chiapense, S. neglectum,
and S. auritum to quite noticeable in S. podophyllum var.
peliocladum, S. macrophyllum, and S.
salvadorense, to noticeably acute in S.
angustatum, S. triphyllum,
S. wendlandii, and S. hoffmannii.
In some species the lateral adaxial margin of the petiole is also
ribbed. This is apparent in S. hoffmannii and S. wendlandii but
especially in S. triphyllum.
petioles of juvenile leaves often differ remarkably from that of
the adult and have a greater tendency to be canaliculate rather
than I-ribbed as in the adult leaves.
leaf blade morphology of Syngonium, as in many other genera
of Araceae, is quite variable. Species often begin flowering before
the full course of maturation takes place in leaf development. For
example, young adult plants may have fewer leaflets per leaf than
older plants. This has created a situation where species have been
described as new because the adult leaves were unlike plants which
had previously been described. The
leaves easily fall into four basic types, and it is along these
lines that the sectional classification of the genus is arranged.
Syngonium.By far the most common leaf type in the genus is
that of section Syngonium with trisect or pedatisect adult
leaf blades. Leaf blades range from the strictly trisect blades
of S. gentryanum to the more highly divided blades of S.
podophyllum, which vary from trisect to 11 -pedatisect. Though
is not necessarily a strict matter of maturity, older, more mature
plants in any population tend to be more highly divided. Any individual
may have considerable variation in the degree of lobing of the leaf
depending on where the leaf occurs on the stem. The higher up the
stem, generally, the more highly lobed or segmented the leaf becomes.
As mentioned in the section on STEMS, the seedling leaves of all
species are entire. Generally the seedling leaves are ovate or elliptic,
and frequently they are also weakly lobed at the base. The intermediate
climbing leaves are always more conspicuously lobed at the base.
The leaves of such intermediate, pre-adult climbing forms are generally
conspicuously hastate or sagittate. It is during this pre-adult
climbing stage that species are most difficult to distinguish from
one another, since nearly all the species in section Syngonium
have leaves that are remarkably similar. However, even at this stage,
differences between species begin to emerge. Some species, such
as S. triphyllum, have posterior lobes that are narrow and are directed
almost perpendicular to the median lobe. The abruptness of change
between an entire leaf with prominent basal lobes and a 3-lobed
leaf varies considerably from species to species. In some species
all intermediate stages are easily found, whereas in other species
the plant seems to switch from an entire pre-adult leaf to a 3-lobed
or 3-parted pre-adult leaf very quickly with no evidence of intermediate
leaf forms. The general pattern of change extend from a more or
less sagittate blade, to a hastate blade, to a 3-lobed blade with
the posterior lobes very constricted near the base. The development
proceeds to where the posterior lobes become lateral leaflets, i.e.,
they become completely free of the median lobe.
lateral segments or leaflets are invariably inequilateral and in
most cases the outer half of the segment or lobe is much wider and
conspicuously auriculate at the base. The degree to which the auricle
develops is very variable from plant to plant, even in the same
species (particularly true of species like S. podophyllum),
but it is often sufficiently consistent in a species to be of taxonomic
development of five or more pedatisect leaves invariably proceeds
with the pinching off of an auricle to produce another segment or
leaflet which in turn goes
through the same process to produce still another pair of segments
degree of separation of the segments or leaflets is an additional
taxonomic character in some species (and not in others). Some species
consistently have leaflets free from one another with exposed sections
of the rachis dividing the leaflets. In morphologically variable
species, such as S. podophyllum, the degree of separation
of the leaflets is highly variable, even at the populational level
with leaves varying from those with united segments to those with
Cordatum.In this section the leaves are entire with generally conspicuously
developed posterior lobes. The overall leaf shape may be ovate or
oblong-ovate or rarely hastate, and the anterior lobe is sometimes
weakly constricted near its base. The section is the second most
common and includes those species (among others) that Engler placed
in his genus Porphyrospatha. Seedling leaves are similar to those
of section Syngonium and soon become ovate-elliptic with
small posterior lobes, but instead of becoming more 3-lobed, they
begin to assume the shape of the adult blade and merely get larger.
In section Cordatum there are no leaves with distinctly intermediate
phases, which are so variable and interesting in section Syngonium.
Oblongatum.-The species in section Oblongatum differ markedly from
all others in the genus because of the oblong to oblong-elliptic
to ovateelliptic leaf blades and petioles, which are broadly sheathed
to the apex with the emarginate free portion of the sheath often
extending beyond the base of the blade. In this section the juvenile
leaves are almost identical to the adult leaves, differing only
in being much smaller. Intermediate stages are much like the adult
Pinnatilobum. -This section is represented by S. steyermarkii,
the only incised-lobate species in the genus. Juvenile leaves are
ovate, soon becoming subcordate at the base and developing sinuate
margins laterally. As the blade matures, it becomes increasingly
more deeply lobed and more conspicuously lobed at the base until
it assumes its adult form, which looks vaguely like the common Philodendron
radiatum Schott with incised-lobate leaves.
blade venation of Syngonium easily characterizes it as a
member of the Colocasioideae. The venation type is the brochidodromous
type (Dilcher, 1974), and the primary lateral veins (i.e., secondary,
see Croat & Bunting, 1979), after extending laterally from the
midrib toward the margin, join into a collective vein which extends
to the apex roughly parallel to the margin. In Syngonium
there are always 3-5 separate collective veins. The primary (inner)
one, being the largest, is initiated by one-of the lowermost primary
lateral veins. Successively smaller collective veins, located at
smaller distances from the blade margin, arise from progressively
lower primary lateral veins or even weak secondary veins branching
off the midrib. Frequently the fourth and especially the fith collective
vein are so near the margin that they cannot be seen with the naked
origin of the primary lateral veins is usually acute near the base,
often becoming more obtuse toward the apex and rarely arising at
nearly right angles to the midrib.
of the characteristics of Syngonium and other members of
the Colocasioideae is the presence of conspicuous reticulate venation.
Tertiary veins can arise from the primary lateral veins (i.e., secondaries)
in which case they orient toward the margin and become parallel
to the primary lateral veins, or they can arise directly from the
midrib. The tertiary veins merge distally and give rise to quaternary
veins. The quaternary veins are found irregularly between the tertiary
veins and at oblique angles, randomly oriented. The quaternaries
in turn give rise to the lowest order of veins, namely the quinary
veins which form the areoles. The areoles are 3-, 4- or 5-sided
and lack a free-ending veinlet. Both the 4th and 5th order veins
are restricted to the adaxial plane of the blade (Birdsey, 1955).
An unusual feature of the quaternary veins of Syngonium and
other Araceae such as Xanthosoma is that they may cross over
a series of tertiary veins before joining with another vein (Birdsey,
cells are often very prominent in the leaf tissue, with two series
of laticiferous cells paralleling each vein, sometimes even up to
the 5th order of veins (Birdsey, 1955).