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Inbotany, afascicle is a bundle ofleaves or flowers growing crowded together; alternatively the term might refer to thevascular tissues that supply such an organ with nutrients.[1][page needed] However, vascular tissues may occur in fascicles even when the organs they supply are not fascicled.
The termfascicle and its derived terms such asfasciculation are from the Latinfasciculus, the diminutive offascis, a bundle.[2] Accordingly, such words occur in many forms and contexts wherever they are convenient for descriptive purposes. A fascicle may be leaves or flowers on ashort shoot where thenodes of a shoot are crowded without clearinternodes, such as in species ofPinus orRhigozum. However, bundled fibres, nerves or bristles as in tissues or theglochid fascicles ofOpuntia may have little or nothing to do with branch morphology.
Leaf fascicles are present in allpines, and the number of adult leaves (needles) per fascicle is an important character for identification of pinespecies andgenera. Most species have fascicles of two to five needles; only occasional species typically have as few as one or as many as six leaves to the fascicle.
Variation is high between species, low within them. For example,Pinus flexilis (limber pine), has fascicles of five needles. This pine is a member of thewhite pine group,Pinus subgenusStrobus, sectionStrobus. In all members of the group the fascicles nearly all have five needles and the sheath at the base of the fascicle is deciduous.
The fascicle sheath is another character that is important for identification. AmongNorth American pines the sheath is persistent in all so-calledhard pines and deciduous in all so-calledsoft pines.[3] Thus, the fascicle sheath and number of needles can be used to identify valuabletimber pines in all seasons and many years before they are mature enough to produce cones. These two characters readily distinguish the major groups of pines (seePinus classification).
Pinus durangensis (Durango pine) has fascicles of six needles, rarely seven, and is the only species inPinus with so many needles per fascicle. At the other extreme,Pinus monophylla has fascicles of one needle, rarely two. This is the only species of pine with just one needle per fascicle, and this rare and easily observed character is reflected in thespecific epithetmonophylla and in thecommon namesingle-leaf pinyon. Although it might strike non-botanists as illogical to apply the term "fascicle" to a stem bearing a single leaf, the justification is that the structure of the stem is consistent with other pine fascicles, which justifies generalising the term to embrace single-needle fascicles as well.
Fascicles do occur in someflowering plants, though not as frequently as in many conifers. Consequently, when fascicles are present the specific epithet often refers to them.
Examples includePrunus fasciculata andAdenostoma fasciculatum. Species with flowers in fascicles includeAechmea biflora andMelicytus ramiflorus, several species ofMalva, and the entire genusFlueggea. Some species of the familyAlseuosmiaceae have flowers in fascicles.
In the Bignoniaceae in the genusRhigozum flowers are borne in fascicles from cushion-like, dwarf branchlets in the axils of leaves, and several species also bear leaves in fascicles on similar or shared branchlets.[4]
Both leaf and flower fascicles occur amongAngiospermae, often asadaptations facilitatingpollination, such as in manyLamiaceae, of which someLavandula are typical. Other plant fascicles are adaptations to achieve greater compactness for defensive reasons. For example, inOpuntia cacti, spines are produced in fascicles bearing a few longspines and many short spiny bristles (orglochids).
Sphagnum species bear branches in fascicles.