17.1–17.3: Three basic tissue types give rise to diverse plant characteristics.

Staghorn cholla cactus and desert brittle bush flowers.

Plants are better than animals. Actually, that’s an absurd thing to say. But only because biology isn’t a contest, and from the perspective of evolution, any species that is not extinct can be considered a success. By many measures, though, plants do surpass animals, having developed a stunning diversity of structures and features during their evolution.

Consider some vital statistics on plants and animals (FIGURE 17-1).

Figure 17.1: In many Important attributes, plants surpass animals.

1. Longevity. The longest-living plants live 10 times longer than the longest-living animals. Bristlecone pines, found in the western United States, can live for more than 4,800 years. Among animals, the ocean quahog (a clam-like mollusk, found off the east coast of North America) can live about 200 years, and giant tortoises, found on some tropical islands, can live almost 200 years.

2. Height. The tallest plants are 20 times taller than the tallest animals. Coast redwoods, found along the west coast of North America, have grown to more than 379 feet (115 m). The tallest giraffe grew to just under 20 feet (6 m).

3. Weight. The heaviest plants weigh almost 20 times as much as the heaviest animals. The largest giant sequoiasare estimated to weigh more than 3,300 tons (almost 3 million kg). The largest blue whales—believed to be the largest animals ever to inhabit the earth—weigh in at approximately 170 tons (154,000 kg).

4. Energy acquisition. Most important is that plants can make their own food by capturing energy from the sun and converting it into a usable chemical form, but animals cannot. Consequently, animals rely on primary producers such as plants for energy. This is why the total amount of plant matter on earth is more than 10 times the biomass of all the animals.

In fact, plants have a host of strategies, vastly different from those that have evolved in animals, for growth, competition, defense, and reproduction. The difference in strategies used by plants and animals illustrates dramatically one of the fundamental truths of biology: there are multiple pathways to evolutionary success.

In this and the next two chapters, we explore the structural and physiological features of plants and how they represent adaptive solutions—often very different from those employed by animals—to the constraints of living on earth. We discuss the three main vegetative structures in vascular plants—the roots, stems, and leaves (FIGURE 17-2)—and how their vascular (or “circulatory”) system works. We discuss plant reproductive structures in Chapter 18.

Figure 17.2: Three distinct plant structures: roots, stems, and leaves.

In later sections of this chapter we explore plant nutrition and the methods by which water, sugars, and other nutrients move from their site of uptake or production to the parts of the plant where they are needed. And we look at some of the cellular specializations in plants that make their unique tissue types possible. First, we look at one important distinction, based on structural differences, that separates most angiosperms—the flowering plants—into two groups.