In botany, a rosette is a circular arrangement of leaves or of structures resembling leaves.
In flowering plants, rosettes usually sit near the soil. Their structure is an example of a
modified stem in which the
internode gaps between the leaves do not expand, so that all the leaves remain clustered tightly together and at a similar height. Some insects induce the development of
galls that are leafy rosettes.
In
bryophyte
The Bryophyta s.l. are a proposed taxonomic division containing three groups of non-vascular land plants ( embryophytes): the liverworts, hornworts and mosses. Bryophyta s.s. consists of the mosses only. They are characteristically limited ...
s and
algae
Algae ( , ; : alga ) are any of a large and diverse group of photosynthetic, eukaryotic organisms. The name is an informal term for a polyphyletic grouping that includes species from multiple distinct clades. Included organisms range from ...
, a rosette results from the repeated branching of the
thallus
Thallus (plural: thalli), from Latinized Greek (), meaning "a green shoot" or " twig", is the vegetative tissue of some organisms in diverse groups such as algae, fungi, some liverworts, lichens, and the Myxogastria. Many of these organisms ...
as the plant grows, resulting in a circular outline.
Taxonomies
Many plant
families have varieties with rosette morphology; they are particularly common in
Asteraceae
The family Asteraceae, alternatively Compositae, consists of over 32,000 known species of flowering plants in over 1,900 genera within the order Asterales. Commonly referred to as the aster, daisy, composite, or sunflower family, Compositae ...
(such as
dandelion
''Taraxacum'' () is a large genus of flowering plants in the family Asteraceae, which consists of species commonly known as dandelions. The scientific and hobby study of the genus is known as taraxacology. The genus is native to Eurasia and Nor ...
s),
Brassicaceae
Brassicaceae () or (the older) Cruciferae () is a medium-sized and economically important family of flowering plants commonly known as the mustards, the crucifers, or the cabbage family. Most are herbaceous plants, while some are shrubs. The l ...
(such as
cabbage), and
Bromeliaceae. The fern ''
Blechnum fluviatile'' or
New Zealand
New Zealand ( mi, Aotearoa ) is an island country in the southwestern Pacific Ocean. It consists of two main landmasses—the North Island () and the South Island ()—and over 700 List of islands of New Zealand, smaller islands. It is the ...
Water Fern (''kiwikiwi'') is a rosette plant.
Function in flowering plants
Often, rosettes form in
perennial plants whose upper foliage dies back with the remaining vegetation protecting the plant. Another form occurs when
internodes along a stem are shortened, bringing the leaves closer together, as in
lettuce,
dandelion
''Taraxacum'' () is a large genus of flowering plants in the family Asteraceae, which consists of species commonly known as dandelions. The scientific and hobby study of the genus is known as taraxacology. The genus is native to Eurasia and Nor ...
and some
succulents.
[Botany online: Features of Flowering Plants – Leaves](_blank)
(When plants such as lettuce grow too quickly, the stem lengthens instead, a condition known as
bolting.) In yet other forms, the rosette persists at the base of the plant (such as the dandelion), and there is a
taproot.
Protection
Part of the protective function of a rosette like the dandelion is that it is hard to pull from the ground; the leaves come away easily while the taproot is left intact.
Another kind of protection is provided by the ''caulescent rosette'', which is part of the growth form of the giant genus ''
Espeletia'' in South America, which has a well-developed stem above the ground. In tropical alpine environments, a wide variety of plants in different plant families and different parts of the world have evolved this
growth form characterized by evergreen rosettes growing above
marcescent leaves. Examples where this arrangement has been confirmed to improve survival, help water balance, or protect the plant from cold injury are ''
Espeletia schultzii'' and ''Espeletia timotensis'', both from the
Andes
The Andes, Andes Mountains or Andean Mountains (; ) are the longest continental mountain range in the world, forming a continuous highland along the western edge of South America. The range is long, wide (widest between 18°S – 20°S ...
.
Smith, Alan P.1979. Function of dead leaves in ''Espeletia schultzii'' (Compositae), and Andean caulescent rosette species. ''Biotropica'' 11: 43-47.
/ref>
Form
The rosette form is the structure, the relationship of the parts, and the variations within it, as shown in the following study from a herbarium:
*'' Dryas octopetala'' (White Dryas, Rosaceae) has a leaf rosette of leaf blades with a short petiole, slim, egg-shaped leaves with cordate bases with clearly and regularly toothed margins, and single flowers on usually long peduncle Peduncle may refer to:
*Peduncle (botany), a stalk supporting an inflorescence, which is the part of the shoot of seed plants where flowers are formed
*Peduncle (anatomy), a stem, through which a mass of tissue is attached to a body
**Peduncle (art ...
s or stalks, two to four centimetres across. The flowers have seven to nine, often even more, white egg-shaped petals. The sepals are lanceolate
The following is a list of terms which are used to describe leaf morphology in the description and taxonomy of plants. Leaves may be simple (a single leaf blade or lamina) or compound (with several leaflets). The edge of the leaf may be regula ...
.[Botany online: Features of flowering Plants – Rosettes – Whorls]
/ref>
*'' Silene nutans'' (Nottingham Catchfly, Caryophyllaceae) shows ensiform-lanceolate leaves. The slightly rosette-like ground leaves are bigger and of different shape than the sparse, opposite leaves on the stem. This is explained in that side shoots with greatly prolonged internodes may spring from rosettes. They have one or more flowers at their tip, like the primrose. Especially in biennial plants, the main shoot can, too, grow with prolonged internodes and even branch. It is not unusual that the leaves of the rosette and those of the shoot differ in shape.
As form then, "rosette" is used to describe plants that perpetually grow as a rosette and the immature stage of plants such as some ferns.
See also
*Asteraceae
The family Asteraceae, alternatively Compositae, consists of over 32,000 known species of flowering plants in over 1,900 genera within the order Asterales. Commonly referred to as the aster, daisy, composite, or sunflower family, Compositae ...
* Bromeliad
**'' Billbergia''
*Fern
A fern (Polypodiopsida or Polypodiophyta ) is a member of a group of vascular plants (plants with xylem and phloem) that reproduce via spores and have neither seeds nor flowers. The polypodiophytes include all living pteridophytes except ...
** Bird's nest fern
** Ostrich fern
** Wild bird's-nest fern
References
{{botany
Plant morphology
Leaves