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Inflorescence Types - MIOS · PDF file6 Spike: Spikes resemble racemes, but bear sessile flowers (sessile: without a stalk; sitting directly on its base). It’s common to hear orchidists

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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.


    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.)

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    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


    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

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