VEGETATIVE TERMINOLOGY
I. Terminology
Taxonomists need descriptive terminology to efficiently and
accurately communicate information. This is particularly important because
taxonomy is, in large part, a descriptive science (vs. experimental science). It
is similar to anatomy and related disciplines in regard to the number of terms
used. Tyson (2001) has written a fun article that argues that some
scientific disciplines, specifically astrophysics, uses less jargon/terminology
than other sciences.
II. Why so much terminology?
The amount of terminology used in Plant Taxonomy may, at
times, seem overwhelming. The following description of 'how they hitch
horses in Europe' from A Tramp Abroad by Mark Twain should hopefully
explain why there is so much terminology.....
The man stands up the horses on each side of the thing that projects from
the front end of the wagon, throws the gear on top of the horses, and passes
the thing that goes forward through a ring, and hauls it aft, and passes the
other thing through the other ring and hauls it aft on the other side of the
other horse, opposite to the first one, after crossing them and bringing the
loose end back, and then buckles the other thing underneath the horse, and
takes another thing and wraps it around the thing I spoke of before, and
puts another thing over each horse's head, puts the iron thing in his mouth,
and brings the ends of these things aft over his back, after buckling
another one around under his neck, and hitching another thing on a thing
that goes over his shoulders, and then takes the slack of the thing which I
mentioned a while ago and fetches it aft and makes it fast to the thing that
pulls the wagon, and hands the other things up to the driver.
III. Phytography
A fancy term for studying the terminology of botany is phytography.
Most terms are derived from Latin or Greek, the language used by scholars during
the early history of taxonomy.
IV. Characters and States
A feature or observable attribute of a plant is called a character
and the specific form or expression of the character is called a state.
For example, flower color is a character with several states including red,
yellow, white and blue flowers. All characters are not equally important for
identification purposes. The most useful features are called "diagnostic"
or "key" characters. These are given more "weight"
when making decisions about a particular taxon. For example, fruits are
diagnostic characteristics in the Mustard family (Brassicaceae); without fruits,
these plants are difficult to identify.
Some characters are rather variable (e.g., leaf
shape, stem height, time of flowering) while other characters are fixed (i.e.,
floral characters). The source of the variation observed in these characters can
either be environmental or genetic. One way to distinguish between them is to do
transplant experiments.
V. Vegetative Terminology
In this section of the course we are interested in terms
related to the vegetative, or non-reproductive parts of the plants. This
includes the three primary organs - leaf, root, stem. Later, we will discuss
terms relating to the reproductive organs (flowers, fruits).
VI. Discussion of Selected Vegetative Terms
We may go into the field (or even grocery store) to observe
and discuss the following terms. The terms in the following list are "fair
game".
A. Life span/Duration:
- annual (completes life cycle in a single year)
- biennial
(completes life cycle in two years; the first year typically as rosette, like
carrot, and the second year it bolts to produce a flowering stalk that grows
quickly)
- perennial (lives more than two seasons)
- evergreen (keeps its leaves
year-round)
- deciduous (looses its leaves at the end
of the growing season)
- caducous - a part that is shed prematurely
(e.g., stipules are often caducous)
Angiosperms (flowering plants) evolved in tropical regions
during the late Cretaceous period. The original (primitive) angiosperms were
likely evergreen perennials
It can be difficult to determine
whether a herbaceous plant is an annual, perennial or biennial. Some tricks
(adapted from Woodland, 1997) are to examine:
- the underground part of part of the plant - annuals have small slender
taproots, while those of biennials and perennials are larger. And,
biennials and perennials often have food storage structures such as tubers
or bulbs
- whether the stem is woody or herbaceous - plants with herbaceous stems
are often annuals, those with woody stems are perennials
- if there are any constrictions or scars where the stem joins the roots -
annuals typically lack these while perennials have them
- the growth form - a plant with a rosette late in the growing season may
be a biennial
- remnants of last year's leaves or stems - the presence of these indicate
a perennial or biennial
B. Plant habit - refers to general growth
form
- herb (herbaceous) - no woody tissue;
e.g., dandelion, sunflower,
goldenrod; herbaceous
- shrub - multiple stems, woody, short;
e.g., honeysuckle,
leatherwood
- sub-shrub (suffretescent) - shrub that
typically dies back to a woody base
- tree - single stem, woody, tall,
e.g.,
oaks & maples
- succulent - very fleshy, juicy stem - cactus
- vine - stem
that climbs or trails, requires support
- liana - woody vines
- forb - non-grass herbaceous plant
Trees and shrubs are woody perennials. Annuals
are often herbaceous.
C. Habitat - refers to environment in
which plant grows
- terrestrial - growing in soil
- aquatic - growing in water;
emergent vs. floating
- epiphytic - plant uses another plant for
support, common in rainforests
- parasitic - plant uses another plant
(host) for water and/or nutrients. Holo-parasites rely completely
on the host and are non-photosynthetic, i.e., non-green.
Hemi-parasites usually are photosynthetic (green) but steal water and
minerals.
- mycorrhizae - fungi that associate with
the roots of plants; facilitate water and mineral uptake
- mycotrophic - plants that rely on fungi
to transfer nutrients to them from another plant; i.e., Indian pipe
D. Plant vegetative organs
- root - anchor and absorbs, underground, positively gravitropic, develop from radicle in seed
- leaf - photosynthetic organ,
attached to stem, has a bud at its base. Leaves are derived from
primordial buds produced by the apical meristem
- stem - leaf-bearing organ,
usually negatively gravitropic, with buds
Some plants lack one or
more of these structures. For example, aquatic plants often lack roots
and cacti lack leaves. There is no clear anatomical distinction
between leaf and stem. The crown is the junction of the root and
stem. A shoot
is a stem with leaves
E. Root types
- tap - one main root - carrot
- fibrous - many roots, no one
root is dominant - grass
- adventitious - a root that develops from a part of
the plant other than another root, like the prop roots of maize or
aerial, climbing roots of ivy
- Storage roots - fleshy enlarged roots
designed for storing nutrients
- haustorium - specialized roots of
parasites for obtaining nutrients/water from a host
- knees/pneumatophores
F. Stem types
- caulescent - standard upright growing stem
- spur shoot - short shoot,
compacted internodes (e.g., Ginkgo, apple)
- rhizome - horizontal,
underground stem - e.g., violet, ginger
- stolon - horizontal above ground stem, also
called a runner, roots at nodes - e.g., strawberry
- bulb - upright, fleshy
overlapping leaves with base attached to small basal stem - e.g., onion
- corm
- upright, hard, surrounded by papery or scaly leaves- e.g., gladiolus
- tuber
- fleshy, with eyes = buds; e.g., potato
- scape - leafless flowering stalk
- cladophyll - flattened, leaf-like stem -
e.g., cactus
- rootstocks - general term for underground
stems such as rhizomes, bulbs and corms
G. Stem features
- node - region to which a leaf is attached
- internode - region between nodes
- axil - junction of leaf and stem
- bud - found in the leaf axil; at
the base
of leaf; embryonic shoot and/or flowers; vegetative buds are responsible for
branching
- axillary (or lateral) bud - buds along
stem, not at end
- terminal bud - buds at the end of
the stem
- bud scales - protective
covering over bud
- terminal bud scale scar - scar left on stem where the terminal bud
scales fell off; can count to determine age of twig)
- stipule scars (scar left
where stipules fall off)
- leaf scar - scar left on stem
where leaf detached
- lenticel - areas on stem, often raised, for gas exchange
- vascular bundle scar - in leaf scar, where
vascular bundle went into leaf
- pith - refers to the central core of the stem. It can
be solid (continuous stuffing), chambered (hollow with partitions = e.g.,
Juglans nigra); or diaphragmed (stuffed with interspersed partitions -
e.g., Celtis occidentalis -
hackberry). The shape of the pith in cross-section can also be a
valuable feature for identification. For example, the pith of oaks (Quercus)
is star-shaped in cross section.
H. Leaf parts
- blade - main photosynthetic part
- petiole - a fancy term for
the stalk
- stipules - appendage at base of petiole in some leaves. Stipules
can be glandular, leafy, spiny, or scale-like. In many cases, the stipules
fall off shortly after the leaf expands. Many plants completely lack stipules
- no stipules = estipulate or exstipulate).
I. Leaf structure
- simple - leaf blade all one section
- compound - leaf blade
divided into smaller sections called leaflets
- leaflet - section of a compound
leaf
- rachis - stalk that supports
leaflets in a compound leaf; central axis
- rachilla - stalk that supports
lateral leaflets
- pinnately
compound
- like a feather
- palmately compound - like the fingers on your
hand
- dissected - leaf divided
into very fine, somewhat indistinct segments
It may be difficult to determine whether a
plant has compound leaves or is a branch with simple leaves. Some tricks include:
- make a cross section of the suspected petiole - if it's round it is likely
to be the petiole, if not, then it is probably a petiolule of a compound
leaf;
- check the branching pattern - if the branches are alternate, even though
the "leaves" appear opposite, then the leaf is probably compound;
- check to see whether the "leaves" are in a single plane or not -
leaflets of a compound leaf are in a single plane, but leaves on a branch
tend to be in different planes;
- check the terminal leaf - the terminal leaf of a branch tends to be offset
from the apex whereas the terminal leaf of a leaflet is truly terminal;
- look for a bud - only leaves have a bud in the axil;
- check for flowers - only leaves will have flowers in the axil;
- check for the color and texture of the leaves and stem - in compound
leaves, the leaflets and rachis are usually similar, whereas the color and
texture of the branch usually differs from the petiole and blade.
J. Leaf attachment & position
- petiolate - leaf with a stalk
- sessile - leaf without a
petiole
- perfoliate - stem appears to run through leaf
- clasping
- sheathing
- base of leaf forms a sheath around the stem
K. Arrangement
Leaves may be found only at the base of the plant (basal, rosette,
as in dandelion) or along the stem (cauline) or some combination. Leaves
are attached at nodes:
- alternate - one leaf per node
- opposite - two leaves per
node; MADCAP Horse is a mnemonic to help remember temperate woody plants with
opposite leaves (M=maple; A=ash; D=dogwood; CAP=Caprifoliaceae or
Honeysuckle family; Horse = Horsechestnut and buckeye).
- whorled - more than two leaves per node;
not common in temperate woody plants
L. Venation
- pinnate - single main (primary)
vein with secondary veins branching from it like a feather
- palmate - several primary veins
arising from a common point
- parallel - primary and secondary
veins parallel to one another
- net or reticulate venation - general
term for pinnate or palmate pattern of veins.
M. Leaf margin
- entire - margin smooth; not common
in temperate deciduous woody plants
- lobed - margin with indentations
like oak
- serrate - margin toothed.
May be singly or doubly (each tooth has a tooth) toothed
N. Special features
- tendril - modified leaf or stem
- thorn -modified stem/branch;
since a stem comes from a bud, thorns are located above leaves. Examples include
apple, pyracantha and Cotoneaster
- spine - modified leaf; below a bud,
like a cactus
- prickles - are from the epidermis; surface features like in roses
O. Surface features
- glabrous - no hairs, smooth
surface
- pubescent - hairy; due to trichomes = hairs
- glaucous - powdery covering;
e.g., Acer negundo, Rhus glabra
- scabrous - rough to the touch like sandpaper
P. Leaf shape
There are many terms to describe the shape of the leaf blade
(linear, oblong, lanceolate, elliptic, ovate, scale-like, needle-like), leaf
apex (acute, obtuse, acuminate, mucronate, truncate, emarginate, rounded), and
leaf base (acute, acuminate, obtuse, rounded, truncate, cordate, oblique,
hastate, sagittate).
VI. Monocot leaves
They are usually simple, with parallel venation, linear and
have a sheath which is considered to be the basal part of the petiole. In fact,
there has been such a severe reduction in the blade that the flattened blade in
many monocots is derived from the leaf base (petiole).
VII. Some general points to consider
- usage of terms may differ slightly from author to author;
- many characters show continuous variation, so the character state may fall
midway between two terms. An analogy would be compass positions; if the
needle points between N and E we call that direction northeast. But what if
it falls between NE and N, and so on? One solution is to combine terms - for
example, linear-lanceolate leaves would have an intermediate shape;
- a single plant may show a range of features (i.e., it could have
some lobed leaves and others that are entire);
- diminutives are often used (i.e., serrulate leaves would have
smaller teeth than a serrate ones); and
- prefixes are often used to clarify meanings. For example, "sub"
means "almost". Thus sub-opposite leaves are not quite opposite.
And "ob" means opposite, such as in obovate leaf shape.
IX. References
- Harris, J.G. & M. W. Harris. 1994. Plant Identification
Terminology: An Illustrated Glossary. Spring Lake Publ, Spring Lake,
UT.
- Cronquist, A. 1988. Evolution and Classification of Flowering Plants.
2nd edn. New York Botanical Garden, NY.
- Tyson, Neil de Grasse. 2001. By any other name.
Natural History. July-August pp 22 - 25.
- Zomlefer, W. Guide to Flowering Plant Families. This book has an
excellent illustrated glossary.
X. Websites
XI. Exercises & Study Hints
- For some study hints and lab exercises -
click
here
- Terms that are "fair game" for the exam
are highlighted in this document.
- Check out the Texas A&M websites and Vascular Plant Systematics
Glossary listed above. They are terrific sources rich with images
and some quizzes.
Last updated:
09/29/2008 / � Copyright by SG
Saupe
