Lecture 5  Angiosperms: Flowering plants

Seeds, Monocots and Dicots

Plant Category Number of known species
Plants that do NOT produce seeds, but grow from spores  (moss, fern, etc.) 150,000
Plants that are gymnosperms (naked seeds NOT enclosed in fruit)  Examples: pine, fir, spruce 1,000
Plants that are angiosperms, division Magnoliophyta.  All flowering plants 250,000
Total of all known plants about 400,000

See Figure 9.1 in Levetin p. 141 for a diagram of relationship among plants.

 1. Angiosperms are flowering plants that produce fruits containing seeds.  (fig 6.2, p. 89-91)

    a.  Seeds are a dormant (sleeping) form of the plant.  They are produced by sexual reproduction and contain stored food and an embryo (developing plant).

    b.  Seed germination or beginning of growth often has certain requirements. Why would it be advantageous for apple seeds to have a cold temperature requirement in order to germinate?  Hint: think about what would happen to seeds that germinated in the fall after the apples ripened.

    c. An extinct date palm has been germinated from a 2,000 year old seed.  See pictures of the  seeds and plant.

 2.  Angiosperm groups: Monocots vs. Dicots

    Angiosperms are divided into two groups, the monocots and dicots. 

    a.  Monocots have one cotyledon or seed leaf that stores food.  As the embryo emerges from the ground, the cotyledon shrinks.  Corn is an example of a monocot.

    b.  Dicots have two cotyledons.  Bean is a dicot.

    c.  Other differences

            There are major differences between monocots and dicots suggesting the two groups diverged or separated millions of years ago.  Current evidence suggests they diverged soon after the appearance of flowering plants, over 100 million years ago.

       

Structure name Monocot Dicot Reference page or figure in Levetin
cotyledon 1 2 91 or fig. 6.2
Veins parallel netlike 41 or fig. 3.10c
Vascular bundles scattered in stem rings on outside of stem 36 or fig. 3.5 a,c
Roots fibrous root taproot 37 or fig. 3.7
Flower parts 3's 4's and 5's 76 or fig. 5.3

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