Mature plants of Pothos
display an interesting
and at times bewildering range of shoot architecture. To date very
few field observations have been made but from what has been done
it is clear that some potentially useful systematic characters are
present. Preliminary investigations of Pothos
can be found in Boyce & Poulsen (1994), Boyce & Nguyen (1995)
and Boyce & Hay (1998).
and P. curtisii
almost the only species for which tolerably comprehensive shoot
architecture observations exist, the following summary can be made.
On germination both species produce an eocaul, a thread-like, cataphyll-bearing
but otherwise leafless, skototropic (shade seeking, see Strong &
Ray, 1975), physiognomically monopodial (see Boyce, 1998) shoot.
The eocaul is capable of extending for a considerable distance along
the forest floor and, at least in the initial stages, although the
green stem is presumably capable of photosynthesis, it appears to
depend partly on food reserves in the large seed. Once a suitable
vertical surface is encountered, the shoot alters its mode of growth
and attaches itself to the substrate by means of short clasping
roots arising from either the nodes and internodes; it can therefore
be termed a root-climber (see Schimper, 1903). At this stage the
juvenile shoot also begins to produce foliage leaves. In P.
) these are similar to
adult leaves in appearance, although more congested and smaller;
the plant is thus homeophyllous. Pothos curtisii
) produces a juvenile root-climber with more-or-less
orbicular imbricating leaves arranged in the manner of the tiles
or shingles of a roof (shingle-climber) and of very
different appearance to leaves produced later in the life cycle;
that species is thus heterophyllous.
Initially all branches produced are adherent. In P.
growth can continue in this manner for a considerable
time, the adherent shoots climbing high into the canopy where conditions
permit and giving rise to branches from older lower portions but
usually not branching distally unless the shoot tip is damaged.
These adherent stems are referred to as mature sterile
in the descriptions to follow. By the time the plant has reached
two or three metres non-adherent irregularly sympodial (i.e. terminating
without flowering) side branches have usually begun to develop.
These branches are plagiotropic, often repeatedly branching to form
extensive curtains of foliage pendent under their own weight and
are referred to below as fertile shoots. It is from the leaf axils
of these plagiotropic branches that the flowering shoots arise.
The juvenile stage of P. curtisii
behaves similarly to that of P.
, the major difference being that the shingle
growth is of limited duration (usually climbing to no more than
3 meters, often considerably less) before the plant abruptly begins
producing leaves of the adult form. The alteration to the adult
form is often accompanied by extensive branching with both adherent
and free shoots arising, and the plant often forming a mass of interlacing
Inflorescences of P.
are solitary and born terminally on non-reiterating
short lateral flowering shoots bearing cataphylls but no foliage
leaves. In other species (e.g. P.
) these lateral shoots can be
elaborated by sympodial branching into leafless, sometimes highly
complex, compact or lax synflorescences (see Mayo et al., 1997)
bearing two to many inflorescences simultaneously or sometimes single
inflorescences in series (e.g. P.
, P. lancifolius
Synflorescences are usually borne along or at the end of leafy branches
or, more rarely on older leafless parts of the stem, sometimes arising
from there (e.g. Bornean and Philippine (Palawan) P. insignis Engl.;
see Boyce & Poulsen, 1994). Very occasionally inflorescences
are solitary and terminal on leafy branches (e.g. P.
A feature of P. curtisii
shared by a number of other species is the production of flagelliform,
leafless (cataphyll-bearing), skototropic, foraging
shoots whose function appears to be to vegetively propagate the
individual by searching for and colonizing suitable climbing surfaces.
These foraging shoots can arise in a variety of positions but are
most often seen at the tips of free or adherent branches.
Certain species (e.g., P. repens
occasionally produce enormously robust reiteration shoots from older,
usually leafless, parts of the plant. These shoots are notable not
only for their size but also for the way in which the leaves are
directed forwards and tightly imbricated and also in the mass of
adherent roots that arise from them. Based on observations of plants
in Vietnam, Boyce & Nguyen (1995) speculated that these reiteration
shoots might serve as a means to rejuvenate ageing plants in which
the quantity of high-climbing stems had become too great for the
functioning root mass.