Rosette (botany)

A rosette ofleavesat the base of adandelion

Rosette growth form of theliverwortRicciocarpos natans.

Inbotany,arosetteis 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 amodified stemin which theinternodegaps 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 ofgallsthat are leafy rosettes.

Inbryophytesandalgae,a rosette results from the repeated branching of thethallusas the plant grows, resulting in a circular outline.

Taxonomies

Many plantfamilieshave varieties with rosettemorphology;they are particularly common inAsteraceae(such asdandelions),Brassicaceae(such ascabbage), andBromeliaceae.The fernBlechnum fluviatileorNew ZealandWater Fern (kiwikiwi) is a rosette plant.

Function in flowering plants

Often, rosettes form inperennialplants whose upper foliage dies back with the remaining vegetation protecting the plant. Another form occurs wheninternodesalong a stem are shortened, bringing the leaves closer together, as inlettuce,dandelionand somesucculents.(When plants such as lettuce grow too quickly, the stem lengthens instead, a condition known asbolting.) In yet other forms, the rosette persists at the base of the plant (such as the dandelion), and there is ataproot.

Protection

Rosette of leaves ofAgave americana

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 thecaulescent rosette,which is part of the growth form of the giant herb genusEspeletiain 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 thisgrowth formcharacterized by evergreen rosettes growing abovemarcescentleaves. Examples where this arrangement has been confirmed to improve survival, help water balance, or protect the plant from cold injury areEspeletiaschultziiandEspeletia timotensis,both from theAndes.

Form

The rosette form is the structure, the relationship of the parts, and the variations within it, as shown in the following study from aherbarium:

• Dryas octopetala(white dryas,Rosaceae) has a leaf rosette of leaf blades with a shortpetiole,slim, egg-shaped leaves with cordate bases with clearly and regularly toothed margins, and single flowers on usually longpedunclesor stalks, two to four centimetres across. The flowers have seven to nine, often even more, white egg-shaped petals. The sepals arelanceolate.
• 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 leaveson 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 theprimrose.Especially in biennial plants, the main shoot can grow with prolonged internodes and even branches. It is not unusual that the leaves of the rosette and those of the shoot differ in shape.

As form, "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
• Bromeliad
  • Billbergia
• Fern
  • Bird's nest fern
  • Ostrich fern
  • Wild bird's-nest fern