Descriptions of Plants
There is a whole language,
drawn from Latin, that is used to describe plants. Some of the words are
familiar, many are not, but when botanists are writing to one another
the words have very precise meanings and are a convenient shorthand, each
one saving a whole phrase that would be needed if the words were not available.
Botanists have established
the ground plan for a leaf as consisting of a broad blade,
on a leaf stalk (petiole) and with two broad places where
the leaf joins the stem which are called stipules. Some
or all of these may be missing. I tell my students that if you
can imagine a variation on a basic plan, some plants have already
Many leaves, perhaps most, do not have stipules. Others do not
have a stalk to the leaf: these are said to be sessile
(seated on the branch).
The croton leaves above
are quite ordinary (in spite of their lurid colours). The begonia
to the left has a palmate shape (like a hand), and this particular
species has the petiole connected to the center of the underside
of the leaf blade instead of to its base. This umbrella-like arrangement
has a shorthand name - we say the leaf is peltate.
Simple leaves are very common:
lilies and most bulbs, grasses,
more than half the shrubs around a typical garden, most of the dieffenbachia/anthurium
family - the list could
be very long.
leaflets is reduced to three.
And these may all come from one point on the petiole - hmmm, feather-like
or hand-like? There is a
term (of course). A leaf
with three leaflets is trifoliolate.
have the blade part separated into smaller pieces.This Peltophorum
leaf has the leaflets coming off what would be the midrib of the
leaf blade. It is a little like a feather in its form: The botanical
term is pinnate.(This leaf is actually twice- or bipinnate
because each leaflet is divided into smaller pieces.)
The blade may also be divided into parts that come from a single
point on the petiole. The term for this is palmately compound,
looking like the fingers of a hand.
Certain plant families
seem to have taken a particular evolutionary track with their leaf
The legume family, for
example, often has pinnately compound leaves, but if you think of
clover, you will see that the number of
Simple or compound ?
It isn't always
obvious at a glance if you are looking at a branch tip with leaves
arranged evenly along its length, or if it is a single large leaf
image to the left is a branch tip with simple leaves
to the right has compound leaves
|Where the leaflets
(green) are attached to the midrib (pinkish in colour), there is no
Where the (purplish) midrib
(now called the petiole) is attached to the branch (also purplish
in colour) there is a bud that could grow out as a branch or as
Look for the bud. This
is the way to tell a leaf from a leaflet.
If a plant has its
leaves on a stalk, there are several ways in which they may be arranged.
Most commonly they are either in pairs, opposite oneanother
on the stem, or they are produced singly in an alternate arrangement.
The two images, left and centre
above, are both of plants with opposite leaves,and because each pair is
at right angles to the pair below it, they are said to be opposite
and decussate Both these are in the mint family where this arrangement
is very common.
The right hand picture is
Acalypha hispida, Red-hot
cat tail, which has an alternate leaf arrangement.
Leaves can also be three at
a node, or several, in which case they are said to be whorled.
||One more situation,
where the plant doesn't have a stem. Here the leaves are in a basal
rosette. I know that this century plant does eventually make a
tall stalk, but that is when it is flowering, and all bets are off
at that point.
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