previous worker has presented a sectional classification for Syngonium.
This may be because until recently, two of the four sections 1 am
proposing had not yet been discovered. Syngonium
crassifolium and S.
schottianum have both juvenile and adult leaves distinctly
different from any species Engler & Krause (1920) included in
their revision of Syngonium, but these two species were placed
in a distinct genus (albeit presumably based on other characters,
see section discussing
the genus Porphyrospatha). Nevertheless, Engler and Krause
did include in their revision two species with adult leaves that
were not the typical trisect or pedatisect leaves of section Syngonium.
These were S. hastifolium,
which in every other respect is like a juvenile plant of
S. podophyllum, and S. reticulatum, now known to be a species
the juvenile phases, which help to understand sectional differences,
were not available to Engler. Nevertheless, the sectional classification
1 am creating is most readily recognized in the adult foliage, although
there are corollary differences in the juvenile and pre-adult phases
divide Syngonium into four sections based on the shape of
the adult lamina.
Syngonium: Leaves trisect or 5-11 -pedatisect. This
section is by far the largest and most variable. It is also the
only section with any truly widespread species. The species exhibit
marked heteroblastic development, with changes in leaf development
in the juvenile, creeping, climbing, and adult phases. These are
described in detail under the heading LEAVES.
Cordatum: Leaves entire and with conspicuous posterior
lobes. This section is the second largest section in the genus.
Some of its species are relatively widespread. All (except perhaps
S. hastifolium) are thick-stemmed, slow-growing hemiepiphytes
that have juvenile leaves similar to the adult forms, only smaller.
section is represented by five species, three of which are restricted
to Central America. Juvenile leaf phases are ovate-cordate and intermediate
stages begin to approach the adult shape with no major modifications.
One species in section Cordatum, S. chiapense, occasionally
has broad, rounded lobes separated somewhat from the posterior lobes.
This tendency to produce auricles at the outer edge of the posterior
lobes is characteristic of section Syngonium and reflects
the relationships of these two sections. Nevertheless, S.
chiapense has the entire, ovate-cordate leaf blades characteristic
of section Cordatum.
Oblongatum: Leaves entire, elongate, the petiole broadly
winged to the apex. This section differs not only in the shape of
its leaves but in having a petiole that is broadly sheathed its
full length with a free-ending ligule extending generally beyond
the base of the blade. Juvenile leaves differ little from the adult
except in size. The section is represented by two species, S.
llanoense from the Isthmian region of Panama and S. armigerum
from Costa Rica.
Pinnatilobum: Leaves deeply incised-lobate; petiole
sheathed to about the middle; juvenile leaf blades entire, more
or less ovate, cordate at the base; intermediate leaves increasingly
incised. The section is represented by a single species, S.
steyermarkii, from Mexico and Guatemala.