Recording-2025-02-21T19:07:42.955Z

Innovations in Vascular Plants

• Evolution of Seeds:

  • Stems of vascular plants enable higher dispersal of spores by increasing height.

  • Special leaves or branches develop sporangia, facilitating the production of more spores.

  • Major innovation occurs with the formation of seeds, enclosing the developing embryo after fertilization of the female gametophyte's egg.

Seed Structure and Function

• Embryo Characteristics:

  • The formed embryo is a diploid structure, referred to as a young sporophyte.

  • Unlike spores, which are single cells, seeds contain a supply of food packed within their structure.

• Seed Dispersal:

  • Seeds can be dispersed, allowing them to grow into new sporophytes.

  • Seed producers include gymnosperms and angiosperms.

Diversity of Seed Plants

• Phylogenetic Tree of Gymnosperms and Angiosperms:

  • Gymnosperms are currently represented by living species shown in light green, while extinct species are indicated in tan.

  • The branching patterns within this tree are uncertain, as denoted by dotted lines.

Evolutionary Adaptations

• Success of Seed Plants:

  • Seeds thrive in drier climates compared to spores, which perform best in consistently wet conditions.

  • As climates became drier, seed-producing plants dominated, leading to their wide success.

Comparison of Spores and Seeds

• Size: Seeds are larger than spores.

• Dispersal Ability: Spore dispersal is generally better; spores can travel vast distances.

• Nutritional Reserve: Spores do not store food; seeds contain significant reserves.

• Water Requirements: Spores typically require a lot of water, whereas seeds require less and can survive short dry spells.

• Growth Rate: Sporophytes grow slowly at first, while seeds tend to grow faster as they have nutrients available.

Gymnosperms' Sex and Reproduction

• Gametophyte Development:

  • Male gametophytes, which are microscopic, develop inside cones. They produce pollen for fertilization.

  • Female gametophytes similarly develop in cones and contain the egg cell.

• Pollination Process:

  • Pollen grains—a form of male gametophyte—are dispersed by wind and require no standing water for fertilization.

  • The pollen forms a tube to deliver sperm to the egg within the female gametophyte.

Lifecycle Dynamics

• Three Generational Structure: A pine seed contains:

  • The embryo (young sporophyte).

  • The mother (female gametophyte).

  • The grandparent (parent sporophyte contributing to cone formation).

Gymnosperm Diversity and Adaptation

• Dioecious vs. Monoecious Plants:

  • Dioecious plants, such as cycads, have separate male and female individuals.

  • Monoecious plants, like pines, bear both male and female cones on the same individual.

• Conservation Efforts: Endangered species like Dade County slash pine remain critically low in numbers due to habitat loss.

Challenges Faced by Rare Plants**:

• Cycads—An Example:

  • A rare Cuban cycad is endangered due to habitat fragmentation and loss of native pollinators.

  • Conservation efforts are in place to preserve and propagate rare species through collaborations and seed banking.

Unique Characteristics of Conifers and Ginkgo

• Characteristics of Conifers:

  • Typically have simple leaves and cones for reproduction.

  • Survive in diverse habitats, showcasing resilience in urban and natural environments.

• Ginkgo (Living Fossils):

  • Morphologically unchanged over millions of years; notable for urban pollution resistance.