Dandelion

Taraxucum officinale Asteraceae /Compositae Including Common Thistle

Dandelions spread out over cracks in the pavement and gravel parking lots as if they were at the beach. The one I drew had unusual colors on some leaves, probably dead or dying because cars kept running over them. Like fall leaves, I assume those colors are usually disguised by chlorophyll when the green leaves are creating sugars. New leaves and flowers continued to form anyway. I love to study this tough plant because I can find plenty, pick, pull apart, and nobody cares. Most of the life cycle can be seen on the same day. Lots of wierd words, beautiful patterns and plenty of questions for next year.

Adaptations: It attracts pollinators with a compact cluster of bright yellow flowers used for a landing place and provides pollen and nectar rewards that help with cross pollination. It can also self pollinate and produce clones by apomixis or create seeds asexually. Even after a mowing, the meristems (where new growth happens) are below the blades so dandelions will just come back with a shorter stature. This lactiferous plant produces a white bitter latex that herbivores probably don’t like. No wonder they are so successful.

Shoots (Roots, Stems, Leaves) The long tap root can create new plants from fragments, store food over winter, and contract to pull the plant below ground level. Basal leaves with lion’s teeth (Dent de lion) form a rosette at the top of the root. This radiating pattern and big teeth give maximum exposure to the sun. Leaves are extremely responsive to their habitat and climate. There are many wonderful terms used to describe their variable shapes, colors and hairs. (See below)

Flowers

Inflorescence: The other family name, Compositae, is more descriptive than Asteraceae because what looks like one flower is really a composite of individual flowers (florets).

Bracts: What looks protective sepals is a whorl (involucre) of bracts that are not sepals but “extra parts” attached to the entire flower cluster. Below left: Two whorls of bracts spreading to reveal the petals. Right: bracts on the left protect an unopened flower while bracts on the right protect a flower that opened, closed and will open when fruits are formed.

Petals and Stigmas: Yellow petals that attract a pollinator are easy to see.  Stigmas receive pollen when ripe and are also easy to see, but you need to make an effort. Below left: yellow petals unfold. Middle: stigmas start to appear. Right: a closeup of the stigmas, like ram’s horns, covered with pollen coming up through fused anthers.

Individual florets. Left below: 2 florets. Five ray or ligulate (ribbon-like) petals that fuse but I can see 5 notches at their tips. They form a tube with one side lengthened that wraps around 5 fused anthers (pollen holders). Inside the tubes are 5 filaments (stamen stalks). The style (pistil neck) lifts the stigma through the anther tube filled with nectar and spreads open ready to receive pollen.  The hairy pappus, that some call the sepals, will help disperse the fruit. The inferior ovary is below all the other parts.

Fruits. Left below: A cluster of several fruits (cypselas) attached to the receptacle (swelling on top of the flower stalk). Right: Individual fruit. A flared pappus lifted by a thin beak on top of one cypsela that was the ovary.

Below left: the receptacle, that looks like a pitted golf ball, still has some cypselas stuck to it. Right: a ribbed cypsela with teeth that point up (muricate) to help the fruit stay in the ground.

One day I went out right after it rained. The water made the radiating shapes formed from hairy pappus, beaks and fruits easy to see at different stages. Right: the receptacle with all the fruits dispersed and surrounded by old bracts.

Name: Taraxacum from a Persian word for bitter herb and officinale means it was used pharmaceutically. Asteraceae comes from the word for star. Dandelions are divided into a subfamily called Lactucoideae and a tribe called Lactuceae or Cichorieae (sources don’t agree) that includes Chicory. They all have only ray flowers and not disk flowers.

Dissections: when I cut across some of the buds I found some wonderful progressions. In the left image, I see new flower clusters about to open. On the right in the same picture, the petals are shriveled, there is more pappus and the ovaries are turning green on top of the receptacle. The right image has the fruits forming. On the right the ovaries/fruits are yellowish and on the left they are much darker and ready to disperse.

Words describing Dandelions.

The more I learn about Dandelions, the more I want to start over next year to “resee” this complicated plant. I think I like my new word “heteroblasty” best.

Heteroblasty: obvious developmental and seasonal changes in form and function including color and indumentum (hairiness) that occur over the lifespan of certain plants. In a word, or two words: “very variable”.

Stem: the tiny stem anchors a rosette of basal leaves alternately attached at nodes with very short internodes (between the nodes).

Leaves: variable because of heteroblasty, I just picked a few descriptive terms:

• Runcinate: large teeth with tips that point down (lion’s teeth).
• Pinnatifed: teeth attached to the midrib like a feather.
• Oblanceolate. Lanceolate means lance-shaped, longer then wide with the widest part below the middle. If you add “ob” it means the widest part is toward the tip. “Ob” is used as a Latin “reverse”.
• Apices (leaf tips): rounded, obtuse, acute or acuminate (come to a tiny point).
• Hairs: indumentum means hairy but there are all kinds of hairs: glabrous (smooth) or glabrate (almost smooth) to sparsely villous, pilose, or villosulous. Villous means long, soft, often bent or curved but not matted. Villosulous means little villous. Pilose is straight spreading hairs.

Flowers:

• Acaulescent or stemless. What looks like the long stem is really a flower stalk or peduncle, like a Pink Lady’s Slipper. More specifically, a hollow scape (leafless flower stalk).
• Receptacle: thickened top of a flower stalk where the florets are attached.
• Bracts: specialized leaves attached to a flower. Each flower head is subtended (next to) two unequal rosettes of bracts.
  • Involucral bracts are a group of bracts shaped like a rosette.
  • Phyllaries (Individual bracts) often used to identify asters.
  • Calyculi outer layer of bracts, little bracts are called bractlets.
  • How bracts unfold: appressed (pressed against but not joined), recurved (bent back), or reflexed (bent back and down).
  • Scarious (thin, dry, membranous, not green)

Inflorescence or cluster of individual florets. Other terms I found:

• Terminal capitulum: compact flower head. 
• Pseudanthium (Greek for “false flower”) sometimes used for Asteraceae head.

Individual florets

• Sepals: some say the hairy pappus forms the sepals. It is white to cream-colored or yellowish to sordid with barbellulate (minutely barbed) bristles. I like the word sordid for a color.
• Petals: each ray floret has a corolla (all the petals) of five united petals with one side lengthened and notched.
• Perfect florets: both male (stamens) and female (pistils) parts on the same floret.
• Stamens
  • Anthers: 5 fused into tube where stigma pokes through.
  • Filaments: 5 hidden in the tube.
• Pistil including ovary, style/stigma
  • A single style (neck) comes up from the ovary and branches into a 2-parted stigma that bends around like ram’s horns to receive pollen.
  • Ovary will become the fruit.

Fruit: A botanical fruit is a ripened ovary and not necessarily sweet.  An achene is a dry fruit that doesn’t dehisce (open). An achene in the Asteraceae Family is called a cypsela. It looks like a seed because the wall of the ripened ovary surrounds and protects a single seed. When ripe, the beak lengthens to help the wind grab the pappus and disperse the cypsela.