AngiospermsRachel Warshaw

Angiosperms: Flowering plants with covered seeds
Angiosperms: Flowering plants with covered seeds

IntroductionAngiosperms, better known as flowering plants, are vascular seed plants that produce the reproductive structures called flowers and fruits. Today angiosperms are by far the most diverse and geographically widespread of all plants. There are about 25,000 known species of angiosperms.
Diagnostic characteristics
  • Heterosporous (Meaning they produce two types of spores differing in size and sex, i.e. the male [microspore] and the female [megaspore], which develop into separate male and female gametophytes) (MB)

  • Produce flowers and fruits

  • They have specialized water transporting cells called vessel elements (MM)

  • Have seeds that are enclosed within the flower/plant (MM)

  • Have fiber (part of the plant) that supports the plant (MM)
  • terrestrial habitats
  • Angiosperms all have been able to live on virtually every habitat on earth. They can live anywhere from deserts to alpine summits, grasslands, freshwater marshes, and dense forests. Many even live in aquatic habitats and can live in salty conditions such as dry lake beds and salt marshes but few are able to live in the ocean. Most marine angiosperms are found distributed in tropical regions and are mostly called “seagrasses”. (CP source 1)

Major types
  • Amborell
    • Only found in New Caledonia, a South Pacific Island
      • Most “primitive” known angiosperm
      • most primitive living flowering plant is Amborella trichopoda (IL)
        • small shrub with tiny greenish-yellow flowers and red fruit (IL)
        • grows in the wild only on New Caledonia, as aforementioned (IL)
        • first species still living to have evolved from unknown common ancestor of all flowering plants, not magnolias or water lilies as previously hypothesized (IL- 11)
  • Water lilies
    • Live in freshwater areas in temperate and tropical climates. (CM)
    • Around 70 species (CM)
  • Other early lineages
  • Divided into 2 groups: Monocots and Dicots. They are named based on the number of seed leaves, or cotyledons that the plants have upon germination. (AP)
        • Monocots
          • Monocots (single cotyledon) have an adventitious root system that contains stems with scattered vascular bundles and flower parts in sets of 3. (AP)
          • Leaves with veins running parallel
          • Ex: lilies, orchids, yuccas, palms and grasses
        • Dicots
          • Dicots (2 cotyledons) have a tap roots system containing stems with vascular bundles in a ring and flower parts in fours or fives. (AP)
          • netlike venation in their leaves
        • Eudicots
          • Includes majority of dicots
          • Ex: roses, peas, buttercups, sunflowers, oaks, and maples
Monocots and Dicots (ZJ)
Monocots and Dicots (ZJ)

Anatomy/Reproductive Structures
Refinements in vascular tissue played a role in the spread of angiosperms into diverse terrestrial habitats. Angiosperms are equipped with xylem cells
Figure 2: Flower anatomy (RK)
Figure 2: Flower anatomy (RK)
called tracheids, which are long tapered cells that function in both mechanical support and water transport. The xylem of angiosperms has fiber cells, which are specialized for support. The third type of xylem cell is the vessel element. They are shorter and wider than tracheids, and they are arranged end to end into continuous tubes that are more efficient than tracheids in transporting water.

The flower is an angiosperm structure specialized for reproduction. A flower is a specialized shoot with four circles of modified leaves: sepals, petals, stamens, and carpels. Sepals are usually green. They are modified leaves that enclose the flower before it opens. Petals are brightly colored in most flowers. They aid in attracting insects and other pollinators. Within the ring of petals are the fertile sporophylls, which are the leaf derived parts that produce spores. The sepals and petal are sterile floral parts, meaning they are not involved in fertilization. There are two rings of sporophylls: stamens and carpels. The stamens are the male reproductive organs, sporophylls that produce microspores that give rise to male gametophytes. They contain a filament and terminal sac (the anther) where pollen is produced. Carpels are female sporophylls, the organs that make megaspores and their products (female gametophytes). A stamen consists of a stalk called the filament and a terminal sac, the anther, where pollen is produced. At the tip of the carpel is a sticky stigma that receives pollen. A style leads to the ovary at the base of the carpel. Protected within the ovary are the ovules, which develop into seeds after fertilization.

A fruit is a mature ovary. As seeds develop from ovules after fertilization, the wall of the ovary thickens. Fruits protect dormant seeds and aid in their dispersal. Various modifications in fruits help disperse seeds. Some flowering plants, such as dandelions and maples, have seeds within fruits that function like kites or propellers, adaptation that enhance dispersal by wind. Many angiosperms use animals to carry seeds. Some of these plants have fruits modified as pods that cling to animal fur. Other angiosperms produce edible fruits. When animals eat the fruit, the animal digests the fleshy part, but the tough seeds usually pass unharmed through the digestive tract. Mammals and birds may deposit seeds miles from where the fruit was eaten

The fruit begins to develop after pollination triggers hormonal changes that cause the ovary to grow. The wall of the ovary becomes the pericarp, a thickened wall of the fruit. As the ovary grows, the other parts of the flower wither away in many plants. If a flower had not been pollinated, fruit usually does not develop, and the entire flower withers and falls away

There are several types of fruits
    • Simple fruit-fruit derived from a single ovary
    • Aggregate fruit-results from a single flower that has several carpel
    • Multiple fruit-develops from a inflorescence(a group of flowers tightly clustered together
Angiosperm Life Cycle (MS 10)
Angiosperm Life Cycle (MS 10)
Above is a diagram that details the anatomy of a typical angiosperm. (MR; Source 13)
Above is a diagram that details the anatomy of a typical angiosperm. (MR; Source 13)

Transport of Materials
Angiosperms are tracheophytes, and vascular plants, so they have vascular tissue to transport materials within themselves. There are two types of specialized tissue: xylem and phloem. Xylem conducts water and minerals upwards from the roots of angiosperms, while phloem conducts sugar and other nutrients from the leaves to the other parts of the plant. Both xylem and phloem are present throughout the plant, rather than in one specific area. (SP)

In order to move nutrients like sugar, angiosperms use pressure-flow. They use energy from ATP to pump sugar into the phloem and concentrate it there. This high solute concentration causes water to enter by osmosis, which creates high pressure levels in the phloem. The high pressure moves the sugar to other parts of the plant. (PS Source 12)
The flower of the sporophytes produces microspores that form male gametophytes and megaspores that form female gametophytes. The immature male gametophytes are contained within pollen grains, which develop within the anthers of stamens. Each pollen grain has two haploid cells. Ovules, which develop in the ovary, contain the embryonic sac. In consists of only a few cells, one of which is the egg.

After its release form the anther, the pollen is carried to the sticky stigma at the tip of a carpe. Although some flowers self-pollinate, most have mechanisms that ensure cross pollination. In some cases, stamens and carpels of a single flower may mature at different times, or the organs may be arranged within the flower that self-pollinate is unlikely.

The pollen grain germinates after it adheres to the stigma of a carpel. The pollen grain, now containing a mature male gametophytes, extends a tube that grows down within the styles of the carpel. After it reaches the ovary, the pollen tube penetrates through the micropyle, a pore in the integument of the ovule, and discharges two sperm cells into the female gametophyte. One sperm nucleus unites with the egg forming a diploid zygote. The other sperm nucleus fuses with the two nuclei in the large center cell of the female gametophytes. This central cell now had a triploid nucleus (double fertilization)

After double fertilization, the ovule matures into a seed. The zygote develops into a sporophytes embryo with a rudimentary root and either one or two seed leaves, the cotyledons. The triploid nucleus in the center of the embryo sac divides repeatedly, giving rise to endosperm (rich in starch and other food reserves)

The seed consists of the embryo, endosperm, sporangium, and a seed coat derived from the integument. The ovary develops into a fruit as its ovules develop into seeds. After being dispersed by the wind or animals, a seed germinates if environmental conditions are favorable. The coat ruptures and the embryo emerges as a seedling, using the food stored in the endosperm and cotyledons

Sexual Reproduction process in Angiosperm (VN)

Environmental Adaptations
  • Refinements in vascular tissue played a role in the spread of angiosperms into diverse terrestrial habitats.
  • These flowers and fruits act as protection of young and pollen. (RJ)
  • Angiosperms will often use mimicry and aposematic coloring to ward off predators.(RJ)
  • Angiosperms often live in environments far from bodies of water. Early species of plants would use water to allow movement of sperm and/or egg. Thus, angiosperms on land have undergone co-evolution with insects and other animals. The insects spread the gametes to allow diverse fertilization of plants.The angiosperm attracts insects, and prevents self fertilization by possessing different colors, fragrances, and nectar. (AR)

Ever since they colonized the land, animals have influenced the evolution of terrestrial plants and vice versa. Plants and animals have been important selective agents on one another. Natural selection favored plants that kept their spores and gametophytes above the ground, rather than dropping them within the reach of hungry ground animals. This may, in turn, have been a selective factor in the evolution of flying insects. Some herbivores were beneficial to plants by dispersing their pollen and seeds. The animals received a benefit in turn, as they fed on specific plants. Natural selection reinforced these interactions when they improved the reproductive success of both partners: the plant got pollinated and the animal got fed.

Pollinator-plant relationships are partly responsible for increased diversity of angiosperms and animals. In most cases relationships between plants and their polinators are less specific than in the extreme coevolution between one plant species and one animal species.
Review Questions
  • Explain how different parts of an angiosperm's flower (sepals, petals, stamen, ovules, etc) aid in the reproductive cycle (Matt B)
  • How has the evolution of sophisticated vascular tissue had an effect on the structure of angiosperms and how they look? (LPE)
  • State all the types of Angiosperms. Discuss the difference between monocots and dicots. (MP)
  • In what ways are angiosperms reproductively more effective than gymnosperms? In what ways are they less effective? (JS)
  • What are the two different types of specialized tissue, and what are their roles? (JP)

1. "Flowering Plants." WAYNE'S WORD. Web. 30 Oct. 2011. <>. (CP)
2. Figure 2.- (RK)
3. "Biology: Vascular Plants Described." CliffsNotes Study Guides. Web. 30 Oct. 2011. <,articleId-8672.html>.
4. (TB)
5. Life: The Science of Biology - David Sadava, H. Craig Heller, David M. Hills (MM)
6. [[ Adaptations| Adaptations]] (AR)
7. Photograph. Sexual Reproduction in Angiosperm. Web. 11 Nov. 2011. <>. (VN)
8. "Angiosperms - Biology Encyclopedia - Plant, Body, Animal, System, Different, Organisms, DNA, Organs, Water, Separated." Biology Reference. Web. 12 Nov. 2011. <>. (AP)
9. (ZJ)
11. Stephens, Tim. "Specimens of Rare Amborella at UCSC Arboretum, 08-30-99." Currents. University of California, Santa Cruz, 30 Aug. 1999. Web. 14 Nov. 2011. <>. (IL)

13. Organ systems. N.d. N.p., n.d. Web. 3 Dec. 2011. <>.