Botany of Stems, Roots, & Flowers

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Stem Parts

• Node - point where buds and branches arise
• Bud - growing point that will develop into a flower or shoot
  • Lateral Bud - buds emerging from the sides of the stem
  • Terminal Bud - bud emerging from the apex (terminus) of the stem
  • (tip: bud arrangement is the same as leaf arrangement: alternate, opposite, whorled)
• Leaf scar - scar left when the leaf falls off
• Lenticel - small corky area that allows for gas exchange
• Pith - the central tissue in the stem

Stem Modifications

(often interpreted as a root but actually a stem modification)

• Stolon - an above ground, horizontal stem, often rooting at the nodes
• Rhizome - an underground stem, typically horizontal
• Corm - short, solid vertical underground stem
• Bulb - short, flat underground stem with fleshy leaves
• Tuber - underground stem modified for food storage

Root Types

• Taproot - primary, central, downward-growing root from which smaller root branches grow
• Fibrous - a many-branched root system with progressively smaller branches

Flower Parts

• Perianth – full outer part of a flower, surrounds and envelops the sexual organs – consisting of the sepal (calyx) and petal (corolla)
  • Sepal (calyx) - not directly involved in reproduction, often we think of as the green part, the lowest whorl
  • Petal (corolla) - not directly involved in reproduction, often we think of as the more colorful part, above (within) the sepals.
• Stamen (male) - often arranged in a third ring around the pistil (within the confines of the sepals and petals).
  • filament - stalk of stamen
  • anther - structure at the top of the filament that contains pollen
• Pistil (female) - often in the center of the flower, may be one or multiple pistils
  • Ovary - where seeds form, produces fruit when mature.
  • Style - is the long tube
  • Stigma - knobby structure on the top of the style

Flower Arrangement

• Perfect Flowers - contain both genders (both male stamens and female pistils present)
• Imperfect Flowers - will only have one gender or the other (either stamens or pistils are missing)
  • Monoecious - flowers imperfect; male and female flowers held in separate structures on the same plant (ex: pine, birch, pumpkin)
  • Dioecious - flowers imperfect; male and female flowers on separate plants (ex: ginkgo, holly, goats beard)
• Solitary - flower occurring singly
• Inflorescence - flowers clustered together in a group – the complete flowering head, includes the stems, stalks, bracts, and all flowers within the flowering head
  • Elongated Inflorescence:
    • Catkin - unisexual flowers, without petals, in a spike-like cluster (Quaking Aspen)
    • Raceme - unbranched with the flowers along the main axis on stalks (White Wild Indigo)
    • Spike - unbranched with flowers connected directly to the main axis (no stalk) (Blue Vervain)
  • Rounded or Domed Inflorescence:
    • Corymb - broad (flat-topped or rounded) with outer flowers opening first
    • Cyme - broad (flat-topped or rounded) with main axis terminating in a single flower that opens first
    • Umbel - broad (flat-topped or rounded) with the flower stalks arising from a single point and resembling the spokes of an umbrella
  • Complex Inflorescences:
    • Head - A dense cluster of stalkless flowers
      • In the head, the ray floret is irregularly shaped; it has a short tube and a strap-shaped limb (in a daisy-like flower, we think of this as a petal).
      • The disc floret is regularly shaped; it has a long tube and a short limb with five lobes (these are the flowers in the center of the head).
    • Spadix - A thick or fleshy, spike-like inflorescence with massed, small flowers and usually enclosed by a bract called a spathe.
    • Panicle - compound inflorescence in which the main axis is branched (ex: meadowsweet)

Fruit

Fruit - a ripened ovary and any other structures which are attached and ripen with it.

Fruits that are dry, but don't split open when mature and contain one seed:

• Achene - Fruits that are dry, but don't split open when mature and contain one seed.
• Samara - a dry, winged fruit containing one seed
• Nut - large, dry fruit with a thick, bony wall surrounding the seed.

Fruits that are dry, will split open when mature and contain multiple seeds:

• Capsule - Fruit derived from multiple ovaries; open to release seeds.
• Silique/silicle - derived from two ovaries; the outer walls of the fruit peel away from a papery inner partition.
• Legume - from a single ovary; opens along two seams.
• Follicle - from a single ovary and opening along a single seam.

Fruits that are fleshy:

• Drupe - flesh surrounds a hard 'stone' which encloses the seeds.
• Pome - outer part is fleshy; center has slightly hardened structures that enclose the seeds.
• Berry - entire fruit is fleshy with multiple seeds; walls may be present inside.