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Glossary of Terms

A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

  Contributors: Marlene Buffington, Nadine Henry, Chris Hoffman, Pat Nelson, Donald Voss, and Lynn Watts

A

 
acuminate
Tapering concavely to a point.
 
acute
Tapering with straight or slightly convex sides to a point.
 
anther
The free end of the stamen that bears pollen; pollen sac.
 
apex
Tip of a leaf or flower.
 
apiculate
Having a short, sharp point.
 
axillary
The angle between the stem and leaf.
 
azalea
Azaleas are found in subgenera Pentanthera and Tsutsusi of genus Rhododendron.  These subgenera are commonly referred to as deciduous and evergreen, respectively.  Azalea leaves are typically thin, flexible while leaves elsewhere in the genus tend to be leathery.  Deciduous azaleas are so called because they drop their leaves in the fall or winter.  Evergreen azaleas have two kinds of leaves: spring leaves emerge at or after time of flowering; summer leaves (usually smaller and somewhat thicker) emerge midsummer and remain on the plant through the winter.  Another important difference is that the terminal buds of deciduous azaleas produce only flowers; those of evergreen azaleas produce new vegetative shoots as well as flowers.

B

bi-generic
Hybrid with parents in two different genera.
 
blade
Extended portion of a leaf.
 
blotch
Area of contrasting color on the uppermost petal(s) of some plants. (See also spotting.)
 
bract
A modified leaf or bud covering.
 
bristle
A slender, stiff hair.
 
bullate
Puckered or quilted appearance.

C

calyx
Outer whorl of floral envelopes, composed of sepals.
 
campanulate
Bell-shaped, cup-shaped.
 
capsule
Seed pod.
 
cilia
Small hairs, often present on leaf margins.
 
clone
A genetically identical plant resulting from asexual propagation (cuttings, layering, grafting, or tissue culture).
 
conic
Cone shaped, conical
 
convex
Curved outward.
 
cordate
Heart-shaped, two rounded basal lobes separated by a deep depression.
 
coriaceous
Leathery in texture.
 
corolla
The floral envelope inside the calyx, composed of a whorl of petals.
 
cultivar
Shortened form of cultivated variety.  A group of plants, selected for particular attributes, that are clearly distinct, uniform, and stable and that retain these characteristics when propagated by appropriate means.
 
cuneate
Wedge-shaped acute angle at the leaf base.
 
cutting
New growth cut for rooting or other vegetative propagation.

D

deciduous
Shedding their leaves at the end of the growing season.
 
declinate
Bent or curved downward or forward.
 
deflexed
Bent abruptly downward.
 
double
Having more than one set of petals or petal-like structures, or with petaloid stamens.

E

elepidote
Without scales, as opposed to lepidote (with scales).
 
elliptic
Oblong with rounded ends.
 
endemic
Native or confined naturally to a given geographical area.
 
epiphyte
A plant growing non-parasitically upon another.
 
ericaceous
Belong to the family Ericaceae, which includes rhododendrons, heathers, mountain laurel, blueberries, etc.
 
evergreen
Bearing green foliage throughout the year.

exserted

projecting beyond, such as stamens projecting from the corolla

F

family
A group of genera sharing certain characteristics.
 
feral
Wild or escaped from domestication and able to reproduce normally.
 
filament
The thread-like stalk of a stamen.
 
flower
The specialized reproductive structure of a seed plant.  Rhododendrons have flowers, not florets.
 
form, pl. formae
A minor variation within a species that is sufficiently distinctive to warrant recognition as a separate taxon.  In cultivated plants, it is current practice to name these forms as cultivars.

G

genus, pl. genera.
A taxonomic group comprising closely related species.
 
glabrous
Hairless
 
glaucous
Having a gray or whitish cast, covered with a bluish, gray, or white bloom.
 
globose
Nearly spherical.
 
grex
All the seedlings of a particular cross.

H

habit
General form of a plant.
 
hardiness
Cold hardiness is the lowest temperature a plant can tolerate without damage.
 
hirsute
With rough or coarse, more or less, erect hairs.
 
hose-in-hose
A double flower having floral envelopes (whorls of petals or petal-like structures) nested one within the other.  The term relates only to appearance, not to the morphology of the structures.
 
hybrid
Usually a cross between different clones within a species (intraspecific hybrid) or between clones from different species.

I

indumentum
A wooly or hairy covering of leaves or young shoots.  Can be on both top and bottom surfaces of new or young leaves, but is usually confined to the underside of mature leaves.
 
inflorescence
An arrangement of flowers on a stem or axis, it may comprise a cluster of flowers or a single flower.
 
involute
Rolled inward or toward the upper side.

J

K

L

lamina
Blade of a leaf.
 
lanceolate
Shaped like a lance head, widening above the base and tapering toward the apex.
 
lax
Not rigid, loose.
 
lepidote
Having scales.  Tiny scales typically cover the undersides of the leaves. Characteristic used to separate the genus rhododendron into two major groups.
 
lobe
A rounded division of a flower or leaf.

M

margin
Leaf or flower edge.
 
mucronate
Having a leaf tip terminating in a hard point that is a continuation of the midvein.
 
mutation
An inheritable change in genetic material.

N

nectary
Nectar secreting gland at the base of the corolla.
 
nervate
Leaves with prominent ribs or veins.

O

obovate
Egg-shaped with the broadest part towards the apex.
 
oblanceolate
Widest near apex, tapering to base, longer than wide.
 
oblong
Much longer than wide, with sides roughly parallel for most of their length.
 
orbicular
Flat with the outline circular or nearly circular; disc shaped.
 
ovate
Egg-shaped with the broadest part towards the base.
 
ovary
Seed bearing part of the pistil.

P

pedicel
The stalk of an individual flower in an inflorescence.
 
pendulous
Hanging down, drooping.
 
petal
One division of the corolla.

petaloid

like or consisting of petals.

petiole
The stack of a leaf.
 
pH
A measure of acidity or alkalinity. A pH of 7.0 is neutral. Smaller numbers indicate acidity, larger numbers indicate alkalinity.   Rhododendrons, like other members of the heath family, favor soils which are mildly acidic with a pH around 5.5.
pistil
The female organ of a flower consisting of ovary, style and stigma.
 
pollen
Minute powder-like grains borne by the anther. Pollen contains the male gametophyte of a plant.
 
precocious
Flowering before the leaves appear.
 
pubescent
Covered with soft, short hair.

Q

quadrate
Square or nearly square.

R

recurved
Curved backward or downward.
 
revolute
Rolled back or downward from the margins.
 
rhododendron
Genus of shrubs in the Ericaceae family (from Greek rhodo meaning rose and dendron meaning tree). In common usage, "rhododendron" usually refers to members of the subgenera Rhododendron and Hymenanthes, as distinct from the azaleas.
 
rotate
Wheel shaped, saucer-like
 
rugose
Wrinkled.
 
rugulose
Lightly wrinkled.

S

section
A division of classification. Sections and subsections are taxonomic groups between genus and species.
 
scale
Tiny, plate-like structures appearing on leaves and other plant parts.
 
sepal
Lower flower part, the calyx.
 
series
A category in an outdated system of rhododendron classification.

sessile

Without a stalk.

 
spatulate
Shaped like a spatula, spoon-shaped or paddle.
 
species
Basic classification unit of plants comprised of individuals that are recognized as distinct from other species, and which can freely interbreed among themselves.
 
sport
A naturally occurring mutation which usually appears spontaneously as a shoot with characteristics which differ from the rest of the plant, such as different flower color, variegated leaves, etc.

spotting

Dots or spots, usually of darker color, sometimes occurring on the upper petal(s) of some rhododendrons and azaleas.

stamen
The male organ of a flower consisting of an anther on a filament.
 
stigma
The tip of the pistil, usually sticky, which receives the pollen for fertilization of the ovule.
 
strigose
Rough with straight, short sharp appressed hairs.
 
subgenus
The principal subdivision of a genus.

suborbicular

Not quite circular

subsection
See section.

T

taxonomy
Classification (based on study of morphology, geographic distribution, phylogeny) and nomeclature. 
throat
The base opening of the corolla.
 
tomentose
Covered with matted, wooly hair.
 
tomentum
Matted wooly hairs on stems, leaves or seeds.
 
truss
Flower cluster (inflorescence) made up of many individual flowers.  The structure varies considerably among species and cultivars, giving the plants distinctive appearance.

U

undulate
Wavy

V

variety
A naturally occurring group within a species that is distinct enough to warrant taxonomic recognition but not sufficiently distinct to be segregated as another species.
 
vein
A vascular bundle in a leaf blade or petal.

W

whorl
Three or more leaves or branches at a node; circle of flower parts as sepals, petals or stamens.
 
woolly
Clad with long, soft more or less or matted hairs.

X

xylem
Tissues in plants through which water and food is conveyed up the stem from the roots, also furnishing support of the plant.

Y

Z


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