Flowering Plants Phylum

Figure 22.12 A. A male cycad with a strobilus. B. Afemale cycad with a strobilus.

Plants PhylumFlowering Night Plants

Figure 22.13 Joint fir (Ephedra). A. Part of a single plant. B. Male strobili, x20. C. Afemale strobilus, x20.

Anatomy Gnetum Images
Figure 22.14 A climbing Gnetum.

Figure 22.13 Joint fir (Ephedra). A. Part of a single plant. B. Male strobili, x20. C. Afemale strobilus, x20.

and in some years, it does not rain at all. The plants carry on CAM photosynthesis, and their stomata are open at night. The plants apparently survive much of the time on dew and condensate from fog that rolls in off the ocean at night.

Welwitschia plants are also truly extraordinary in appearance. The stem rises only a short distance above the ground's surface and is in the form of a large shallow cup that tapers at the base into a long taproot. The plants may live to be 100 years old and at maturity have a crusty, barklike covering on the surface of the stem cup. The stems may be more than 1 meter (3 feet 3 inches) in diameter (Fig. 22.15).

Throughout their life span, Welwitschia plants usually produce only two leaves. The leaves are wide and straplike, each with a meristem at the base. The meristems constantly add to the length of the leaves, but as the leaves flap about in the wind, they become tattered and split, wearing off at the tips so that they are seldom more than 2 meters (6.5 feet) long. Welwitschia is dioecious, with both male and female strobili being produced on axes that emerge from the axils of the leaves. This makes the strobili appear to be growing around the rim of the stem cup.

Figure 22.15 A female Welwitschia plant in the Namibian Desert. Photo by Margaret Marker, in the collection of the National Botanical Institute, Kirstenbosch. Courtesy Fiona Getliffe Norris.

432 Chapter 22

Chloroplasts Figure

Figure 22.15 A female Welwitschia plant in the Namibian Desert. Photo by Margaret Marker, in the collection of the National Botanical Institute, Kirstenbosch. Courtesy Fiona Getliffe Norris.

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