The Lower Taxa
For this presentation, the Lower taxa of plants are those below the Angiospermae or Flowering Plants.
These plants are treated separately due to their fairly limited chemistry, a result of their paleotypic origins. Many of these plants we find to be remnants of much larger phylogenetic groups developed millenia ago as a natural part of the evolutionary process. A few of these groups are still of considerable size in spite of their age and the major changes that have taken place in the environment since their initial development. Of these taxonomic groups, the largest in terms of biomass is perhaps the Conifers (Pinopsida), and the largest in terms of both genus and species the Ferns (Filicopsida).
The chemistry of these groups is fairly scattered and was more than likely a great deal more complex when these plants were more dominant within the ecosystems. In general, the ethnobotany is therefore fairly limited for these groups compared with others, but still important to assess in relation to each other and to later evolved plant groups.
Comparing the “All Plants” Pie in the lower right corner and the Angiospermae in the upper left, the dependency mankind has on Angiospermae for phytochemicals and their products is obvious. If we trace the food sources (green wedge) we see a fairly high percentage of this value in nearly all of the major plant groups (up to 100% of the uses in fact).
This is especially true for Filicopsidae (Ferns), and of course there are other uses for ferns that occasionally appear ranging from medicines to some materialistic applications (fiber, etc.); the use of fern parts for a dye is possible, though not noticed in this review. If we go to other sources for ethnobotany-related uses (a later topic of review really for this overview), we find that there are significant amounts of use of ferns for specific cultural or ethnic group settings. When Filicidae are reviewed in more detail at the Order level on down, some unique features appear and are noted in the more detailed tables that are produced for these plants.
The best way to develop a better understanding of the Ferns in relation to all four levels of chemical significance, it is safe to assume that in many cases some Fern genera are very well-developed in terms of anti-insectivoric and anti-molluscic agent effects–these chemicals deter leaf, pileus and rhizome feeders. But for the most part, ferns are fairly structural in their chemical make-up, with well-developed applications to highly humid and water-rich ecological and environmental settings, as well as to aerie and xeric tree canopy conditions and periodic drought ecosystems.
The addition of toxicity to food related uses in Equisetopsida is noted. There is a nicotine pathway evolved in this division, although the levels of this neurotoxin are very low. Still, the presence of this alkaloid suggests the possibility that other members of this Division once existed that had well-developed nicotine pathways. This fits the ecological setting in which these plants exist. The major organisms impacted by the nicotine would probably be members of the insecta and other exoskeleton-bearing animal groups.
The next level up, Cycads, produce some potential foodstuffs other than leaf, stem and rhizome products. Cycads produce starch-water storage systems in need of protection. This the evolution of non-protein amino acid (npaa) cycadotoxins (blue wedge). These are very important chemicals in Cycad species, most important Level 3 and Level 4 chemical additions to their chemical evolution arsenal.
We find some of the Cycad pathways partially inferred in the next plant group up–the Pinopsida or Conifers–but the pathways used to generate these chemical are very different, and in a way more complex. Whereas simple amino acid production followed by modification was required to produce the npaa’s, in Pinidae, there is an unusual alkaloid path that forms this plant’s toxins, and in the more advanced family of Taxales, a very specific alkaloid synthesis pathway at work to produce the alkaloid taxine.
One of the interesting things evolutionarily speaking about Pinopsida and it predecessors mentioned, is that two possible pathways to protection again insecta are evolved. The neurotoxin path, and the physical feeding deterrent (terpene resin-producing) path.
In lower groups that are non-woody, we see the development of various forms of neurotoxic agents, most fairly specific to the early evolved neurotransmitter paths–ephedrine is autonomic-sympathetic-adrenergic; nicotine is nicotinic-parasympathetic-acetylcholine receptors. The npaa’s of cycad are toxic along a variety of pathways, some complete different from the other groups. The neurotoxic cycasin works in pathways related to the limbic system in the brain, the area where norepinephrine and serotonin receptors are at play. This may suggest an evolution for toxins effective on animals with a much more complex development of their nervous system.
The alternative to toxins are the terpene-resin producing pathways, a feature more typical of conifers. The resins are poly- and oligoterpene compounds that are capable of producing a fairly thick fluid used to fill, and then protect a wound site against penetration by organisms. This substance captures the organism, and although it does have some aromaticity that could possible keep organisms away, relies mostly upon the resin to capture its feedants and prevent bacteria and other microorganisms from entering its biologically active xylem and phloem tissues.
The most important to feature to note here is the curious nature of the terpenes in this class of plant products. For the most part, the current hemispheric differences define the type of resin a Pinidae produces. Northern hemisphere resins are slow drying and tend to remain tacky or sticky even once hardened. Southern hemisphere resins tend to dry completely and become brittle, capable of fracturing once they are completely dried. These physical differences are due to a simple bond difference–left hand versus right hand, in the production of the poly and oligoterpene compounds.
In spite of these toxic chemical features for Cycads and Pines, there are medicinal uses for these two groups. Chemical diversity has now led to a differentiation of potential medical uses for plants within the same group. Whereas the medicinal values of ferns rely heavily upon the much smaller chemical differences, and those of the upper groups more limited by their simplicity in chemical form and make-up, the increasing chemical complexity of the Pinidae in terms of its N-pathways (pinine and taxine alkaloids, the neolignan epipodophyllotoxin (in Calocedrus), and taxols, vs. nicotine and other highly selective but simple aminotoxins), its reliance on terpenoids of all molecular sizes, lengths and bond forms, and its development of the flower and seed storage organ, change some of the underlying uses for its members, in potential varieties of medical and toxicological applications at the medicopharmacy level.
The Ginkgo group has even more structural, environmental and ecological features added to its chemistry. The fruit structure and it putrid smell, the development of more interesting flavonoids, the modifications of its leaf and woody structures, all point to more sophisticated development of structures and their chemistry by making more effective use of systems already in place, and then adding to their complexity and methods of interaction with other environmental features or beings. Ginkgo has its own wood, food, medical and toxicological features due to these changes.
Gnetopsida is to some the link between the other Gymnosperms and the Angiosperms. Immediate observation of is appearance suggests it very much resembles the angiosperms. It lacks much toxicity (of course we are only talking about one species here). It seems closely related to the ephedra and wyethia of other monogeneric paleobot groups nearby. It still ahs some ethnobotanical use and limited environmental and ecological involvement in its natural environment. It is structurally sound in the right settings, lacks toxicity, and lacks much specificity in terms of chemical content. It is primarily adapted to its setting as a Level 3 plant, with limited Level 4 involvement due to this chemical simplicity.
The remaining large group–the Angiospermae–define the bulk of the plants and their uses. They are a group on their own in need of review, in two parts. Suffice it to say that these two groups show a tendency to continue to evolve along the same chemical pathways already seen with the lower taxa. There is an increase in chemical complexity, increase in medical use types and increase in numerous other chemical features measured in plants as well, ranging from protection based pathways such as phenolics and oxygenated terpenoids, to more complex, selectively toxic chemical production at all levels possible.