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Ed. Note: Back in (nearly) the ancient history of this publication, a few offerings
about botanical terms were published for novice members. The following one
originally appeared in Vol. 3(7): 5-7 (2002).
In ordinary conversation most humans tend to generalize, and use slang words
and clichs, but the language of science is exact, descriptive, and meticulous. If the
words seem strange, the problem is not with science, but with the habit of careless-
ness in general conversation. These definitions, from July, 2002, are reviewed,
updated, and embellished particularly for the benefit of newer members.
Inflorescence Types
Inflorescence: the arrangement of flowers on a floral axis; a floral cluster.
Inflorescence Types
General: Before discussing inflorescences, another term, rachis, needs to be de-
fined. A rachis (ry-
kiss) is (1) the axis
of a compound leaf
or fern upon which
the leaflets are at-
tached; or (2) the
major axis of an
inflorescence. That
said, Correll and
Johnston (1970)
define the term in-
florescence as the
flower cluster of a
plant, or, more cor-
rectly, the disposi-
tion of the flowers on an axis. Dressler (1981) simplifies this to the flower (if
solitary) or flower cluster of a plant. More simplistically, the inflorescence is that
specialized structure that holds the flowers. However, there are different types of
inflorescences, and at this point, specialized terminology enters the scene. Intro-
ducing this plant part, six basic types of inflorescences are shown here (Fig. 1).
These are not all the inflorescence types, but theyll do for a start. In addition, in-
florescences are differentiated as terminal or lateral by the location from which
they arise on the plant. An inflorescence produced at the apical end of the shoot or
pseudobulb is called terminal. Lateral inflorescences arise from nodes near the
pseudobulb base, the sides of stems, or from leaf axiles or opposite leaf axiles.
It should be understood that just because one species of a genus exhibits a cer-
tain inflorescence type or flowers terminally or laterally, not all members of the
genus necessarily have the same habits. Maxillariella tenuifolia, for example, pro-
duces single flowers, but Camaridium (used to be Maxillaria) densa produces its
flowers in a panicle. The key here is that we are trying to define the inflorescence
itself, not trying to generalize it to any genus. Remember: just because a species of
The MIOS Journal 14(3): 2-8. 2013. Ferry, R. J.: Inflorescence Types.
Fig. 1. Diagrammatic representation of inflorescence types.
3
Paphiopedilum, Maxillaria, or a species of another genus is mentioned as bearing
flowers a certain way, doesnt mean all members of a genus will do the same.
Single: The single type of inflorescence is seen in Paphiopedilum species as well
as in members of Lockhartia, Lycaste (Fig. 2), Maxillaria, Miltonia, and other
orchid genera. In passing,
note that the Lycaste conso-
brina provides an example
of single flowering as well
as demonstrating lateral
flowering; arising from the
pseudobulb base. As an
aside, it may also be noted
that L. consobrina flowers
begin opening prior to the
new vegetative growth
sprouting. Note also the
rather dehydrated condition
of the pseudobulbs. In their
normal annual growth cycle,
the vegetation grows; the pseudobulb then forms below; and then the leaves ma-
ture, wilt, and are discarded. The plant then enters the winter or dry season as
only a cluster of pseudobulbs. These gradually dehydrate and as their internal sug-
ars coalesce, flowering is initiated with the onset of the wet-season or spring
rains. The flowers open and are hopefully pollinated, followed soon by the new
vegetative growth. As the wet-spring gives way to the slightly drier summer
season, the seed capsules mature. As the winter-dry season sets in, the capsules
dehisce and the powdery seeds are blown to new locations to (hopefully) sprout
with the onset of the following spring-wet season.
Head or Composite: The term head should actually
be labeled composite. It may appear to be seen in a
few orchid species where the flowers are densely
packed on the inflorescence, but orchids dont utilize
the composite mode of flowering. Dicots do. Members
of Asteraceae (the Aster or Sunflower family) and the
Fabaceae (Bean or Legume Family) are good exam-
ples. In the monocot Orchid family, we dont see the
composite flowering form, but its included here mere-
ly as an example of one of the inflorescence types. Some orchid species do cluster
their flowers terminally, but they do so as an umbel modification or a panicle, not
a head or composite.
A ready example of a head inflorescence is seen in Red Clover (Trifolium prae-
tense L.), a widespread wildflower (a member of Fabaceae, the bean family; Fig.
3). Members of the Aster (sunflower) family also produce the classic composite or
head which actually contains many individual flowers, each of which produces a
The MIOS Journal 14(3): 2-8. 2013. Ferry, R. J.: Inflorescence Types.
Fig. 2. Lycaste consobrina. Note the lateral flowering from the base of the pseudobulb.
Fig. 3. Red Clover. (Trifolium repens L.)
4
single seed. The yellow petals around a sunflower heads circumference are not
petals at all, but ray
flowers. In older books
the reader may run
across the name
Compositae for the
Family Asteraceae, and
Leguminosae for the
Family Fabaceae .
These are obsolete
terms for these families.
Several years ago, the
international congress
of botanists agreed to
change these family
names as listed in the
International Code of
Botanical Nomenclature
in order to reflect
a more correct
viewpoint of
each family.
Thus, correctly
speaking, the
Asteraceae is the
Aster (not Sun-
flower) family
and Fabaceae is
the Bean (not
Legume) family.
Umbel: This type
of inflorescence
is well illustrated
by members of
the Asclepidaceae (Milkweed family), Gentianaceae (Gentian family), and Apocy-
anaceae (Dogbane family). Observing closely, it will be noted that the inflorescence
is actually a group of flower clusters or umbels held terminally on the stem. Casual-
ly, the whole inflorescence is sometimes referred to as an umbel, but it might be
better termed an umbel of umbels or a compound umbel. This type of inflo-
rescence is typically seen in the Butterfly weed (Fig. 4).
Another attractive example of the umbel type of inflorescence may be seen in the
flowers of an aquatic, The Floating Heart,Nymphoides aquatica (Gmel.) Ktze.
(Fig. 5). This perennial is known from ponds, lakes, and slow streams in Florida
and coastal plain of Georgia west into Louisiana and eastern Texas. One suspects it
The MIOS Journal 14(3): 2-8. 2013. Ferry, R. J.: Inflorescence Types.
Fig. 4. Asclepias lanceolata (Asclepidaceae). (Butterfly Weed, Chigger Weed) Umbel type inflorescence.
Fig. 5. Nymphoides aquatica (Gmel.) Ktze. (Gentianaceae). (Floating heart) Umbel inflorescence
5
would readily acclimate in ponds in the Rio Grande Valley. In some orchid spe-
cies, occasionally the axis of a spike can be leaf-like, and the flowers are borne on
a structure called a phylloclade.
This umbel modification, the
umbellate raceme, occurs in
Bulbophyllum (Fig. 6), Cir-
rhopetalum, Epidendrum, Mal-
axis (Fig. 7), and Microstylis.
Asclepias lancolata and other
members of the milkweed fami-
ly are frequented by Monarch
butterflies which also lay their
eggs on the plants. As the cater-
pillars dine on the leaves, they
ingest the poisonous milky sap.
This otherwise poisonous sap
doesnt harm the caterpillars,
and it is passed on to the ma-
ture butterflies. As a result, a
young bird eating a Monarch
butterfly very shortly discovers
that eating this particularly col-
ored insect causes a severely
upset stomach. The result is the
young bird learns to leave mon-
archs alone! The Viceroy but-
terflys caterpillar does not dine
on milkweeds, and hence the
Viceroy remains a tasty meal
for a bird. However, its colora-
tion imitates the Monarch well
enough to deceive the bird-
predators, and it gets left alone
as well. This phenomena is
known as Batesian mimicry. By
the way, as a note to humans
inclined to examine the flowers
of Butterfly weed and handle
them in the wild: theyre also
known as Chigger weed, and
an encounter with chiggers that
have gained access to the hu-
man body, particularly in the
underarm, joint, and groin areas
is not soon to be forgotten!
The MIOS Journal 14(3): 2-8. 2013. Ferry, R. J.: Inflorescence Types.
Fig. 7. Malaxis corymbosa Umbel type inflorescence. 35mm slide #040900-1. Km 17-20 area, ca. 1500m.
Mexico, Nuevo Len, Hwy Santiago Laguna Sanchez