Early seed plants in the genus Elkinsia are a sister group to a clade consisting of gymnosperms and angiosperms. Draw a phylogenetic tree of seed plants that shows Elkinsia, gymnosperms, and angiosperms; date the branch points on this tree using fossil evidence. (See Figure 26.5.)

Short Answer

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Phylogenetic Tree of Seed Plants that represents Elkinsia, gymnosperms, and angiosperms are shown below:

Genus Elkinsia is a fossil plant, and it originated 360 million years ago. After that, about 350 million years ago, the first seed plant was developed named gymnosperm, for example, Lycophytes, horsetails, ferns. In 200 million years ago, the angiosperms plants were formed that developed seeds along with the flower.

Step by step solution

01

Evolution of plants

The DNA sequence is specific to each organism. Several mutations are not passable from successive generations. Somatic mutations are caused by the genetic change that occurs in somatic cells. Mutations in the germline can be handed down across generations and can develop in reproductive cells.

02

Evolution of gymnosperm and angiosperms Plants 

Gymnosperms survived when the climate dry, thanks to their fundamental terrestrial adaptations, including seeds and pollen, found in all seed plants.Furthermore, due to their needle-shaped leaf's thick coatings and limited surface surfaces, many gymnosperms were especially suited to dry regions.

According to recent fossil discoveries, several gymnosperms were pollinated by insects more than 100 million years ago—the earliest evidence of insect pollination in any plant group. Angiosperms began to supplant gymnosperms in some habitats late in the Mesozoic.

03

Phylogenetic tree showing Elkinsia, gymnosperms, and angiosperms

Seed plants were first discovered in 360-million-year-old remains of plants of the genus Elkinsia. These and other early seed plants existed 55 million years before the first gymnosperm fossils and almost 200 million years before the first angiosperm fossils. It is not known which extinct lineage gave rise to the gymnosperms because these early seed plants disappeared.

The earliest fossils of gymnosperms from an ongoing lineage date back is 305 million years. Lycophytes, horsetails, ferns, and other seedless vascular plants characterized these early gymnosperm habitats in the Carboniferous period.

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Most popular questions from this chapter

As will be described in detail in Concept 38.1, the female gametophyte of angiosperms typically has seven cells, one of which, the central cell, contains two haploid nuclei. After double fertilization, the central cell develops into endosperm, which is triploid. Because magnoliids, monocots, and eudicots typically have female gametophytes with seven cells and triploid endosperm, scientists assumed that this was the ancestral state for angiosperms. Consider, however, the following recent discoveries:

  • Our understanding of angiosperm phylogeny has changed to that shown in Figure 30.14b.

  • Amborella trichopodahas eight-celled female gametophytes and triploid endosperm.

  • Water lilies and star anise have four-celled female gametophytes and diploid endosperm.

(a) Draw a phylogeny of the angiosperms (see Figure 30.14b), incorporating the data given above about the number of cells in female gametophytes and the ploidy of the endosperm. Assume that all of the star anise relatives have four-celled female gametophytes and diploid endosperm.

(b) What does your labeled phylogeny suggest about the evolution of the female gametophyte and endosperm in angiosperms?

Explain how the pine life cycle in Figure 30.4 reflects the five adaptations common to all seed plants.

Compare and contrast a pine cone and a flower in terms of structure and function

Contrast how sperm reach the eggs of seedless plants with how sperm reach the eggs of seed plants.

If a seed could not enter dormancy, how might that affect the embryo’s transport or survival?

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