A consequence of being on the edge of a tectonic plate is the presence of a diverse set of mountain ranges with a bizarre range of geologic phenomena. This has created a landscape with countless combinations of microclimates, soils, and moisture dynamics that have pushed plants in innumerable evolutionary paths. California’s mountain ranges create rain shadows that keep our desert landscapes dry. They are responsible for the alluvial soils of the central valley and drastic elevation changes that bring rain and snowmelt from mountaintops to lower elevations. These mountainous waterways host plant communities of their own with species that are adapted to the abundant source of moisture. These highly productive systems are host to over a quarter of California’s land mammal population as riparian plants contribute an immense quantity of food and shelter to these organisms.
Fig A: Merced River, Yosemite National Park
In addition to being highly productive, riparian plant communities form the boundary between two ecosystems. Known as a transitional community, plants that tolerate the drier conditions distant from waterways form a mosaic with plants that are strictly riparian as one community meets the other. This creates a blending effect where a high degree of biological diversity is observed. As mammals seek the resources from this abundant plant community, so do birds and butterflies. The richness of butterfly species drastically rises in response to the riparian ecosystem plant diversity, since an individual butterfly will associate with one species of plant. Birds follow a similar pattern but are not as exclusive as butterflies. Birds exploit the dense riparian forest canopy. As they spend most of their time in the trees, a plant community with lush foliage and a myriad of dwellings will support a more rich bird population, allowing various species to occupy different niches. This phenomenon is known as niche partitioning. Finally, the dense root systems stabilize riverbeds, promote sedimentation, control erosion, and mediate runoff into the aquatic environment.
The morphological variation in the plant kingdom is daunting and often discourages the layperson from developing an appreciation for its complexity. Many understand the terms herb, shrub, tree, or vine. But there are many intermediates between these narrow classifications that, once understood, will broaden one’s perspective on plant structure and development. The first step to understanding plant diversity is to conceptualize morphological variation and broaden the idea of plants fitting into distinct categories (i.e. shrub or tree). All plants possess organs. These organs form the basis of variation as different species have differing morphology in these structures. Roots, shoots, stems, leaves, flowers, and fruit are just a few organs that form the basis of this variation. Each of these morphological variables differs from species-to-species. The following is an analysis of these variables, illustrating the range in diversity among the plant kingdom.
Plant habit: The general form of a plant
-Herb: plants made primarily of parenchyma (see “Foothill” section for details on cell types) cells. Shoots die back at the end of an annual growth season. May be perennial or annual. Perennial herbs generally die back to an underground storage structure (i.e. rhizome, tuber, bulb, etc.) and resprout the following season. These plants are known as geophytes.
-Shrub: a perennial, woody plant that sends many branches out from ground level.
-Subshrub: a short plant that is woody at the base and sends out herbaceous shoots.
-Tree: a tall, woody perennial plant having one main stem that branches arise from
-Vine: a climbing plant that grabs onto object with structures known as tendrils. Woody vines are known as lianas
A vine wrapping its tendril around a support structure.
Plant life form:
-Rheophyte: plants found along the banks of streams and rivers.
-Saxicolous: plants found growing in the cracks of rocks.
-Geophyte: perennial plant that dies back to an underground rootstock.
-Epiphyte: plants that grow on other plants (i.e. many orchids)
-Halophyte: plants that have adapted to salty conditions.
-Succulent: plants with fleshy stems and leaves that store water in large vacuoles.
-Mycotroph: plants that receive nutrients from a fungal associate.
-Xerophyte: plants that are adapted to resource limited conditions. (often dry, hot, and infertile).
The “Joshua Tree”(Yucca brevifolia) is a well-known xerophyte
Root types; variations on the common root structure:
-Taproot: one, long primary root within small lateral roots branching from the structure (carrots, burdock, etc.)
-Fibrous root system: no main taproot. All roots are generally thin and sprawl out from a single point underground.
-Contractive roots: roots that contract vertically. Onion roots, below the bulb, actually do this.
-Haustoria: roots of parasitic plants that tap into the host’s vascular system (thinking Dracula and fangs!)
-Pneumatophores: roots that grow upwardly from the soil for access to oxygen.
-Buttress roots: thickened and enlarged roots that meet the trunk above ground and stabilize heavy plants in loose substrate
The shoot system; variations on the common stem:
-Thorn: a sharp pointed stem or shoot (i.e. cacti)
-Scape: a stem-like structure arising from basal (ground level) leaves with flowers at the top.
-Rootstocks: underground stems that accumulate storage compounds. Plants that die back (i.e. herbaceous perennials) remain alive underground and resprout from rootstocks.
-Rhizome: a horizontal underground stem (i.e. ginger)
-Corm: a spherical underground stem (i.e. water chestnut)
-Bulb: another spherical underground stem. Less stem tissue than a corm, but has numerous layers of succulent and leafy storage tissue (i.e. onion)
-Caudex: trunk-like, short and thick stem
-Tuber: a thick underground and starchy storage stem (i.e. potato)
-Stolon: often called a “runner”, it is a stem that runs parallel to the ground surface (i.e. strawberry)
The “runners” of the strawberry plant
-Rain shadow: dry areas of lower elevation that are adjacent to high mountains where rain is blocked for much of the year.
-Alluvial soil: clay, silt, or gravel deposited where rivers or streams terminate. It is generally very fertile and desirable for growing crops.
-Productive: high rates of photosynthesis and energy cycling in an ecosystem. Often associated with diverse and abundant systems.
-Richness: total number of species in an ecosystem.
-Niche partitioning: two competing species utilize the same resource by occupying different areas with comparable access to the desired resource.
-Denaturing: breakdown of a protein’s structure through chemical or temperature stress.
-Critical load: amount of mineral nutrients that plants can extract from the ground. Important for agronomists who seek to understand crop demands for ecological and economical conservation.
Species on Display
-Schoenherr, Allan. A Natural History of California. Berkeley: University of California Press, 1992. Print.
-Peter Raven, Ray Evert, and Susan Eichhorn. Biology of Plants. Sixth. New York: W.H. Freeman and Company, 1999. Print.
- Simpson, Mike. Plant Systematics. 7th. Burlington, MA: Elsevier INC., 2010. Print.
- "Ecosystem Services." World Resources Institute. N.p.. Web. http://www.wri.org/project/mainstreaming-ecosystem-services/about
-Calflora: Information on California plants for education, research and conservation.
[web application]. 2008. Berkeley, California: The Calflora Database [a non-profit organization].
Available: http://www.calflora.org/ (Accessed: Oct 20, 2008).
-All photographs: Creative Commons Attribution