Reproduction and Life Stages
Text Box: Mature sporophyte Dandelion (2n) Text Box: Anther Male (2n) Text Box: Ovary Female (2n) Text Box: Meiosis Text Box: Mitosis Text Box: Mitosis Text Box: Microspore (1n) Text Box: Pollen grain (1n) (male gametophyte)

Wind dispersion
Text Box: Megaspore (1n) Text Box: Meiosis Text Box: Female gametophyte (1n) Text Box: Pollination

Fertilization
Text Box: Zygote (2n) Text Box: Seed (2n) Text Box: Developing Sporophyte

(1) A mature dandelion contains a mix of male and female parts within the flower head.  (2) The female part (ovary) and the male part (anther) go through meiosis, which is the dividing of the diploid into haploid spores. (3) The female spore (megaspore) and the male spore (microspore) enter mitosis, which creates duplicate spores of each (4) now making the male and female gametophytes. (5) The male and female gametophytes are still located within the flower head, insects cause the pollen to enter a nearby female gametophyte. (6) With the male and female together, double fertilization (look below for more details) occurs to form the zygote. (7) The zygote grows and forms a seed.  (8) The seed is then wind dispersed and lands in the soil. If the seed lands in an accurate environment condition, the stem (taproot) starts to grow into the soil and the sporophyte starts to develop into a mature dandelion

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Wind dispersion

Before the dandelion turns yellow, the flowers are enclosed within a bud (Figure 1).  The bud opens during the day light, exposing the yellow flower head (Figure 2). During the open phase, each flower petal unrolls exposing the stalk containing the pollen.  The pollen can then be transported by an insect to the ovule to create a seed.  Dandelions can even pollinate themselves in cases when the bud does not open due to lack of sunlight. The seeds develop within the bud and start to push up through the top of the bud.  The seeds continue to grow and form fluffy, white sprouts (Figure 3).  Now the seeds can be wind dispersed to grow a new dandelion.

Figure 1

Figure 2

Figure 3

DOUBLE FERTILIZATION

 

Dandelions fall under the major lineage in plants called angiosperm.  Angiosperms are the only plants that go through a process called double fertilization.  The insects that land on the dandelion stir around the pollen on the anther, causing it to fall onto the stigma of the carpel.  The pollen contains three nuclei, one that is for direct growth and two that are used for fertilization.  Once the pollen drops into the stigma, it creates a tube down the style into the ovary for the pollen to flow down to reach the egg.  The pollen contains two grains, one for each fertilization.  One fertilization occurs by  entering the embryo and creating a zygote.  The other fertilization occurs by the pollen entering the endosperm (3n) which is used as a nutritional source for the embryo.

THREE MAIN STAGES

Which one are you most familiar with???