Notes on Flower Reproduction, Fruits, Seeds, and Dispersal

Flower types, reproductive structures, and plant sexuality

• Stamens and pistils define male vs female floral parts; a single flower can have either or both.
• Monoecious vs dioecious:
  • Monoecious: plants bear both staminate (male) and pistillate (female) flowers on the same plant. Examples given: corn, wild rice, hemp, hop, buffalo grass.
  • Dioecious: stamens of flowers borne on separate individual plants (separate male and female plants).
• Specific examples mentioned:
  • Monoecious: corn, wild rice, hemp, hop, buffalo grass.
  • Dioecious (staminate on separate plants): hemp, hop, buffalo grass.
• Solitary flowers: a single flower born singly on the stalk. Example provided: tulip.
• Inflorescence vs solitary flowers:
  • Inflorescence = flowers in multiples or clusters; noted as the typical form in agronomy for many crops.
  • Solitary and other flower forms are more often discussed in horticulture due to aesthetic value.
• Perfect flowers (flowers with both male and female parts) are generally not the focus in agronomy; more discussion in horticulture because of aesthetics.

Inflorescence prevalence in agronomy and horticulture aesthetics

• In agronomy, the majority of crops are evaluated as inflorescences (e.g., strawberry, wheat, oats, and other grasses).
• Horticulture emphasizes perfect flowers and aesthetics (landscaping value).
• Examples of ornamental flowering plants discussed: azalea bush, magnolia tree, rose bush.
• Aesthetic purpose of flowering plants: visual appeal, landscaping decisions (e.g., why people plant and maintain rose bushes with thorns).

From fertilization to fruit: definitions and implications

• Fertilization leads to fruit formation.
• Fruit definition: the mature ovary plus its associated parts; generally the seed-bearing organ.
• Parthenocarpic fruits: seedless fruits (formed without fertilization).
  • Examples mentioned: naval oranges, some figs, and seedless varieties like seedless watermelon.
  • Reason for seedless fruits: consumer convenience and market demand; seedless fruits can command different prices
    and are often marketed for easier eating.
• Can a watermelon reseed itself? Yes, under the right conditions, a plant can self-seed and germinate from remaining fruit/seed in the environment.
  • Note: modern cultivation often relies on deliberate replanting; natural reseeding can occur but may be unreliable depending on conditions.
• Seed dormancy and reseeding in practice:
  • Some plants are more designed to reseed themselves (e.g., some clovers or weeds) than others; seeds can persist in soil until conditions are right for germination.
  • Example anecdotes: tomato seeds germinating in a greenhouse after a plant dies; ryegrass can germinate with minimal soil contact when moisture is available.
• Fruit purpose: to protect and disseminate seeds.
• Seed dispersal mechanisms and vectors:
  • Dispersal by defecation (birds and other animals).
  • Wind dispersal (e.g., milkweed).
  • Water and ocean dispersal (as noted post-hurricane observations in marsh areas).
  • Human-mediated dispersal and accidental spread discussed via anecdotal observations after severe weather events.
• Simple versus aggregate versus multiple fruits:
  • Simple fruit: formed from a single ovary of one flower.
  • Aggregate or multiple fruits: formed from several ovaries; multiple fruits develop from many individual ovaries.
  • Examples of multiple fruits/aggregates (from a single stalk): blackberries, strawberries, figs, pineapples.
• Pericarp and related structures:
  • Pericarp = the wall of the fruit; includes layers such as exocarp, mesocarp, and endocarp.
  • The orange, lemon, lime, grapefruit illustrate citrus fruits with multiple carpels and locules (sacs) containing seeds.
  • The interior sacs of citrus fruits are composed of carpels that house seeds.
• Pepos (berries with a thick outer rind, derived from the ovary):
  • Example fruits formed from interior carpels with a thick rind include cucumbers, melons, and squashes.
• Dry fruits that do not split open at maturity (indehiscent): listed as examples include corn, rice, wheat, barley, walnut, hickory, and carrots.
• Nutrition and variety in fruits:
  • Different fruits provide different nutritional profiles; a varied diet is recommended to obtain a broad range of nutrients.
  • The nutritional value is tied to the type of fruit and the tissue that is consumed (flesh, seeds, and edible parts vary by species).

Seed anatomy and germination

• The seed contains the mature ovule with an embryo.
• Embryo definition: miniature plantlet formed within the seed via the union of male and female gametes during fertilization.
• Two growing points during germination:
  • Radical: the root portion that grows underground.
  • Plumule: the shoot portion that grows aboveground.
• Germination triggers:
  • Water and soil contact initiate germination; some seeds require only moisture, others require more soil contact.
• Seed storage parts and nutrition:
  • Endosperm, cotyledons (also called seed leaves), or perisperm serve as food storage for the developing seedling.
  • In cereal grains, the endosperm is a major storage tissue.
  • Common edible seeds include corn, beans, and sunflower. Depending on processing, you may eat the seed coat as well.
• Seed coverings and dormancy:
  • Seed coats can be hard or soft, and some seeds have dormancy that makes them long-lived in the soil.
  • Goatweed: a weed example highlighting long-lived seeds and persistence in disturbed soils; seeds can remain dormant for extended periods.
• Weeds and garden implications:
  • Bermuda grass mentioned as a weed in gardens but desirable in hay meadows; reflects the context-dependent desirability of certain species.

Seeds, storage, and seed diversity: practical considerations and questions

• Seeds play a central role in human civilization; concept introduced: seed diversity and seed storage locations are important topics.
• A prompt/question raised in the lecture: Where do we store seeds for humanity? Hint of a location in Norway (seed storage discussions historically reference seed banks in Norway).
• Assignment prompts mentioned:
  • Why do we need seed diversity? Consider ecological resilience, crop breeding, and food security.
  • If you don’t want to use a phone, you can use classroom computers for completing the assignment.

Connections to broader topics and practical implications

• Agronomy vs horticulture:
  • Agronomy emphasizes inflorescence and seed production for crops; horticulture emphasizes ornamental flowers and aesthetics.
• Reproductive strategies influence management:
  • Monoecious and dioecious species affect breeding programs, pollination requirements, and crop planning.
  • Seedless varieties (parthenocarpy) affect consumer preferences and market economics.
• Seed biology informs nutrition and food systems:
  • Understanding seed storage tissues (endosperm, cotyledons, perisperm) explains why certain grains are central to diets.
  • Diversity in fruits and seeds supports a varied diet and nutrient intake.
• Environmental and ecological implications:
  • Seed dispersal methods (wind, animals, water) influence plant distribution and invasion potential.
  • Disturbance (e.g., hurricanes, soil disruption) can alter plant communities by releasing or redistributing seeds.
• Practical gardening and farming tips reflected in lecture:
  • Don’t rely solely on self-seeding; environmental conditions determine success of reseeds.
  • Weed management must consider seed longevity and persistence in soil.

Quick recap of key terms to study

• Monoecious, dioecious, staminate, pistillate, solitary flower, inflorescence
• Simple fruit, aggregate fruit, multiple fruit, pericarp, endocarp, mesocarp, exocarp
• Locules, carpels, parthenocarpy, seedless fruits
• Embryo, radical, plumule, germination
• Endosperm, cotyledons, perisperm
• Seed dormancy, seed dispersal vectors (birds/defecation, wind, water)
• Reseeding vs deliberate replanting; weed persistence (e.g., goatweed, Bermuda grass)
• Seed diversity and seed banks/location considerations