Monday, July 13, 2015

Plants vs. Animals

"Befriend the plants and give them aid..."
-Pierre de Ronsard, 1578

I am currently reading In Praise of Plants by Francis Halle'. His central premise is that people have a preference for animals (and he argues that they should reconsider that). I think this is true in general, but like all generalities it isn't true for everyone. After all, the great Linnaeus himself had a preference for plants. When I think back to my earliest memories of nature, I was about equally interested in plants and animals. I grew up in Ventura County. My parents liked to picnic and fish on the weekends, so we were often at places like Wheelers Gorge, the old Lake Matilija (before the dam was cut down), Lake Cachuma, and Lake Casitas. These areas are surrounded by oak woodlands and chaparral. The creeks leading into the lakes have lush riparian woodlands. There were lizards, water striders, ferns, fish, miners' lettuce, sagebrush, quail, sycamores, willows, cottonwoods, dragonflies, tadpoles, and always the massive, gnarled trunks and spreading limbs of coast live oak.

Lake Casitas, Ventura County, photo courtesy of Thewellman
To me, plants and animals, rocks, water and air were always inseparable. That why, when the concept of ecology came to my attention around 1967 it made perfect sense to me. I mean, of course everything is linked together in an interdependent system. How could it possibly be otherwise? It turned out to be a lot more complex than I imagined, but the basic idea has remained unchanged. When we moved into our current house in 1989 I started planting some native California plants. But I didn't just want to have native plants - I wanted to try to emulate an ecosystem that I have loved all my life. That means not only growing the right plants but also emulating natural processes. I'm still working on it.

But getting back to Halle', he studied architecture as well as botany, giving him some unique insights into the architecture of plants, especially trees. The branching of stems, arrangements of leaves on the stem, structure of flowers, placement of flowers, and behavior of roots are not random but governed by genetic programming, as Mendel first elucidated for us. Architecture is a fitting term to describe the process by which plants achieve their genetically programmed size and form. 

For example, tree growth is a trade-off between two very strong tendencies - the tendency towards verticality and the need to maximize surface area of leaves. He estimates that a tree 40 m tall could have a leaf surface area of 10,000 sq. meters (1 hectare). Sometimes on a sunny day I look at the 20 year old coast live oak in my front yard and wonder how many leaves it has at any one time. I have no idea what the answer is, but I like to image them as so many tiny factories, inhaling air and absorbing photons from the sun, converting them to sugar for energy and cellulose for plant tissue. I also think about how long it might live. It should easily outlive me. If someone doesn't harm it, it could easily live into the 22nd century. I like to imagine one of my grand children, or even one of my great-grand children (not born yet) living in this house with this oak tree in 2115.

My oak tree today with the beginnings of its architecture
Halle' also talks about plant movement. Although they can't travel, plants do move a lot - just really slowly. I have always been fascinated by time-lapse photography of plants because it makes it possible for us to see their movement on a time scale that makes sense to us. With the motion speeded up, we see leaves angling themselves toward the sun, flowers opening and closing, stems elongating and jockeying for position. Because they can't travel to attract mates or escape predators, plants have evolved chemical means of doing so. Plants are fabulous chemical laboratories, full of attractive scents and flavors as well as powerful toxins. Again I think about the oaks. Since they are wind pollinated, they have no need for insects to deliver pollen, and yet they are great attractants for insects. Oaks do need a little help spreading their acorns around, notably from squirrels and birds. Below are three photos of the insects that I have seen around my oak tree.

Bark Lice
Some kind of "walking stick" insect
Orange Sulphur Butterfly
The relationship between plants and insects could be described as "complicated", like a human couple that can't decide if they can live with each other or not. Plants lure insects with their colors and fragrances, and in so doing they make insects the unwitting agents of the plant's reproduction. But if the plant is a "host" plant for the insect, then the insect lays it eggs on the plant and thus the plant becomes the unwitting agent for the reproduction of the insect.  The insect's eggs hatch and the larvae of the insect proceed to eat the plant. In the first case the relationship is mutually beneficial. In the second case, the plant is clearly the loser. But in the really, really big picture plants also benefit from this arrangement. Plants and insect can't really live without each other.

Syrphid fly on Tidy Tips
Plants have much greater genetic plasticity than animals, meaning that they produce more mutations and are less troubled by them. One reason for this is that, lacking a true circulatory system, harmful mutations do not spread throughout the entire plant and threaten to kill it. At their worst they merely condemn the meristem that they are part of, leading to the death of a branch, for example. The ability to generate and tolerate mutations ultimately benefits plants. Halle' describes it as "a reserve of variability that plants need to survive in a fluctuating environment from which they cannot escape..." In the love/hate relationship between plants and insects, the ability of a plant to produce mutations throughout its potentially long lifetime enables it to keep pace with the evolution of insect species that may produce hundreds (or even thousands) of generations in the same time span.

Similarly, plants hybridize much more readily than animals, and the resulting offspring are often endowed with so-called "hybrid vigor" or heterosis. Not surprisingly, plants are better than animals for displaying this phenomenon. The greater genetic variability of plants allows hybridization to occur with fewer undesirable effects. Without going into detail (which I don't understand anyway), hybrid vigor appears to result from canceling out genetic "noise" that is naturally present in all species (ScienceDaily, July 22, 2010). Another author gives several examples of plants' ability to use polyploidy ,another form of genetic variability that animals don't easily utilize, to adapt to soils that would otherwise be toxic (Introduction to California Soils and Plants, Kruckeberg, 2006).

In his closing chapter Halle' describes the Two Faces of Botany. There is Botany, the scholarly pursuit which values data and precision, producing a great amount of knowledge but perhaps missing out on some of the intangibles such as beauty. Then there is botany which he describes as "unofficial and alternative, one fully alive and abundant, burgeoning, suckering, polymorphous, and multicolored, eclectic, unclassifiable, erotic, pagan..." While I appreciate the knowledge generated by Botany and I try to understand as much of it as I can, botany is my true love. It's why I prefer gardening to research. As a result, I'll always be an amateur and I'll never know as much as I should, but Halle' has helped me understand that's okay.

I'll finish up with a few things that are blooming now.

Justicia purpusii, Chuparosa. Cape region of Baja
Euphorbia lomelii (formerly Pedilanthus macrocarpus) Slipper Plant or Candelilla. From central and southern Baja.
The flower does look like a slipper.

Ruellia californica ssp. californica, Rama Parda. Also from central and southern Baja
Hazardia sp. from the Channel Islands. There are two species, cana and detonsa and they look very similar.
I don't know which one this is.
Munzothamnus blairii, Blair's wire lettuce. From the Channel Islands.
Epilobium canum ssp. canum (formerly Zauschneria californica). Just starting to bloom now. Loved by hummingbirds.

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