Thursday, March 26, 2015

Dichotomous key (V) - Bud scars

Leaf scars have personality. No doubt about it. With a nice little bonnet, top hat, or beehive hair do to cap off a gnomish face, each monster marches a terrifying procession along the length of their twigs. These tiny monsters grin out at the unsuspecting world. And lo, a peripatetic naturalist pauses to discover their intricate world. Sam and I spent some time asking these trees what their names were and boy were we discovered. Each face is a leaf scar, the outline of where the stalk of a leaf connects to twig. The dots and features that give the face its facey-ness collectively form the vascular bundles, which are composed of xylem and phloem (imagine cutting a celery stalk in cross section). 

(Black locust) Marrowzodufia Blugly the Dwarf

(Butternut) Pompuzador the bonnet keeper of spiggetiezi

(Yellow birch) Joy Doom Happy Stacks

(Cottonwood) Mark Buntly of the Broofing Haws

(Common buckthorn) Ronald the Masked Parasitic Jubilee

(Slippery elm) Squirky Bunkles

(Staghorn sumac) Salwall Dimlar the Jay Slorper

(Sugar maple) Starky Cusperbun

(Lilac) Ralphez the woggly-eyed lime top

(Black cherry) ZanKiffle Waffletragedy, aka ZK Waffles in the forests of Burlington

(American beech) Qwayzar Dalooskie

(Bitternut hickory) Ahab Dilbous-Bannister, Purveyor of Simple Fun

(Quaking aspen) Emperor Mewslies of Nostralias
(White ash) The Honorable Wide Collared Professor Kitten Anderson
(Witch-hazel) Slippy Ghoul Grin aka Barbara Butterfields aka Babs Buttfiel

Monday, March 23, 2015

Dichotomous key (IV) - Pith

Pith is one of my favorite things for some reason. I think its substance remained elusive to me for a long time - I couldn't seem to track down a good answer as to what it was and why it looks the way it does for different species. Over the years, primarily through carving, I've become much more acquainted with pith. Pith is essentially the undifferentiated, highly moldable ingredient of new growth. Also called medulla (which means middle), it also stores starches and water.

Classification of plant cells narrowing down to pith (I didn't subdivide alternate branches of the classification)
  • Vascular tissue (transport water, nutrients)
  • Dermal tissue (protection, prevent water loss)
  • Ground tissue (photosynthesis, food storage, growth/regeneration, structure, protection)
    • Sclerenchyma (main structural support of plants)
    • Collenchyma (structural, provides extra strength in areas of new growth - think, the long fibrous strands in celery)
    • Parenchyma (play a large role in synthesized food and water storage)
      • Chlorenchyma (photosynthesis, home of chloroplasts)
      • Aerenchyma (large intercellular spaces that hold air for buoyancy and respiration)
      • Prosenchyma, or Palisade parenchyma
      • Vascular parenchyma (forms either the xylem or phloem)
      • Medullary or ray parenchyma
      • Conjunctive parenchyma (root parenchyma)
      • PITH!

Pith changes in a variety of ways over time, the most obvious of which is color. Most pith starts as whitish in color and changes as it dies and ages to a yellowish or brown. The above photo shows this years growth of staghorn sumac on the left. Note the single growth ring of white adjacent to the egg yolk yellow spongy pith. On the right, below the bundle scars from the previous year, is a two year old section of the branch showing the darker brown aged pith. Note here the white ring of sap wood and the previous year of woody growth in the single ring of yellowish wood.

Turtle-like pattern of poplars

Cottonwood showing fluted ridges that correspond to the vascular bundles connecting to the leaves
Pith doesn't have a ton of variability in terms of shape in cross-section, so this isn't often a helpful tool for identifying the species. But some are beautifully non-circular. The Populus genus has five-pointed stars in cross section. The above photo shows a cottonwood (Populus tremuloides) twig in cross-section. The five-pointedness of the pith on cottonwoods corresponds quite nicely to the five ridges running parallel lines on outside of the twig.

Chambered pith of white walnut - or butternut (Juglans cinerea) above and black walnut (Juglans nigra) below
The walnuts have perhaps my favorite pith. Above is both black and white walnut pith side by side. For others the pith disintegrates completely (one way to distinguish between native and non-native honeysuckles is to crack open a twig; non-native honeysuckles are hollow, as shown in the photo at the top of the posting).

From top to bottom, Staghorn sumac, catalpa, elderberry, white ash

Some species have fantastically huge pith. Particularly great examples of these include elderberry, ash, staghorn sumac, catalpa, boxelder are among these species. Other species have nearly invisible pith.

Wednesday, March 18, 2015

Dichotomous key (III) - Of twigs both stout and thin

White ash on left surrounded mostly by red maple in the background, note the ashes much stouter branches
Leaves have typically fallen off the tree in the fall (except on trees that died before the fall or marcescent  trees or evergreen trees), so we can't see if they're simple or compound. But looking at the twig can give us some indication of what they might have been. I know I said that relative characteristics aren't the best, but they can be helpful with gestalt (recognizing something on a subconscious level) and I'll try and add numbers in to support this. 

Stand of staghorn sumacs showing thick twigs (also support the heavy fruit stalks that are persistent)

Compound leaves can be thought of "cheap disposable branches" (Peter Thomas's description in the incredible Trees: their natural history). This allows the trees to put more investment into quick vertical growth rather than into developing energy intensive branches lower down the bole. A somewhat contradictory result is that compound leaves are bigger and therefore weigh more, and so need a more robust twig to support them. Therefore, we might ascertain from looking at a twig if it's simple or compound. While I'm focusing on opposite twigs here, some of the thickest twigs are the alternate compound leaves of sumac.

Butternut on left, staghorn sumac on right. Both have compound leaves attached to stout twigs
Below I've broken down which of the MAD Capped Bucking Horse species are simple and which are compound:

  • Maples (except boxelder)
  • Dogwoods
  • Caprifoliaceae (except elderberry)
    • e.g. Viburnums, Honeysuckles
    • Boxelder (Ash-leaf maple)
    • Ashes
    • Elderberry
    • Horse chestnut 

    I went ahead and did some homework and gathered twigs from most of these species. I arranged them in order of increasing diameter, and wouldn't you know it, this corresponds to relative leaf size! In the photo above, from L to R, we have honeysuckle, buckthorn, dogwood, red maple, sugar maple, norway maple, boxelder, white ash, elderberry. This wasn't exactly a perfect sample, but I did try to find "average" twigs.

    Okay, so in a rough estimate, we have the following:

    Relative twig diameter
    (1=smallest, 9=largest)
    (s=simple, c=compound)
    Leaf size
    (from Peterson's Eastern Trees)
    Honeysuckle (s)
    Glossy buckthorn (s)
    Red-osier dogwood (s)
    Red maple (s)
    Sugar maple (s)
    Norway maple (s)
    Boxelder (c)
    White ash (c)
    Common elderberry (c)
      It works out quite nicely, at least in my minimum little experiment. I'll be it would be more instructive to measure twig diameter in the summer and measure the weight of all the leaves attached to that twig. But for now, I'm satisfied with the results. 

      Thursday, March 12, 2015

      Dichotomous key (II) - opposite (and sub-opposite)

      Decussate opposite branching - each pair offset 90deg in sugar maple (Acer saccharum).

      This post is mostly a reiteration and expansion of some of the notes from the previous post on branching patterns. There are relatively few trees/shrubs that have opposite branches. If we have an opposite or subopposite species we can use the mnemonic MAD Capped Bucking Horse. Usually it's just MAD Cap Horse, but since we're using shrubs here too, I called it a MAD Capped Bucking Horse.

      Horse chestnut

      Boxelder (Acer negundo) with branches offset at about 90degrees
      Both alternate and opposite branches can have the nodes arranged around the stem in another pattern. The first, and far more common, is called decussate. Decussate branches have nodes at right angles to the pair above and/or below. By alternating placement, the tree maximizes the amount of light each branch receives.

      Winged euonymus (Euonymus alatus) branch tending towards distichous branching
      Distichous branches, on the other hand, run in two parallel lines up the branch. We don't have any distichous opposite branched trees in Vermont. It's a common growth pattern in understory trees that tend to arc out and flatten at the top, like musclewood or hophornbeam, in order to maximize access to sunlight. If you're growing vertically it doesn't make a whole lot of sense as this would shade out the leaves/branches below.

      If you're growing mostly vertical, it makes sense to be decussate (branches offset 90deg), but for branches that flatten out, reaching to the sides of the bole, or trunk, for sunlight, a distichous pattern makes a whole lot of sense. While out today I noticed that the lowest branches on sugar maples are showed a functional distichous pattern. That is, for the most part, they had cut off growth of branches that grew along a vertical plane. I noticed on white ash that I looked at afterwards that the branches were mostly following this pattern, and in places where the vertical branches were still growing, the one away from the sun tended to be significantly longer. That way it could still harness sunlight while not shading out leaves adjacent to it.

      Here in Vermont, we only find pronounced sub-opposite branching in buckthorns (common buckthorn, as shown above, and glossy buckthorn shown on the previous post). The faster a twig grows, the more offset are its paired buds. This can even be seen in species other than buckthorns. Once I started looking I noticed this on ash, though the distance they're offset was at most negligible. Glossy buckthorn appears primarily alternate. 

      Tuesday, March 10, 2015

      Dichotomous key (I) - Branch pattern (phyllotaxis)

      Opposite apical buds on winged euonymous (Euonymous alatus)

      Dichotomous: Dikho (Greek: two, apart) + -tomia (Greek: cutting)

      Given my familiarity with the gross anatomical features of twigs, I was ready to dive into identification by learning the specifics. It would be in my ability to discern variation in the different features that would allow me to use a dichotomous key and identify the twig of concern. A good dichotomous key is indeed a rare thing. Many field guides (most tree ID books) lack them because they often require highly technical language, making them difficult for neophytes (pun intended) to use. But they are incredibly useful as they force the observer to look and look again. Making good dichotomous keys (for anything) requires the following:
      1. Finding categories that you can use to lump the things you're studying into the largest groups possible. These categories will have to be binary. For humans, you might start with something like gender, or eye color. You wouldn't start with obscure characteristics, like has four fingers since this would give you two very uneven sized groups.
      2. Avoid relative characteristics (like big, frail, etc.) and be specific with numbers where possible
      3. Come up with characteristics that have only two answers. Essentially, you're creating two groups repeatedly until there's only one item in each group. So blond and not blond, male and not male
      4. Start with easy to observe characteristics. Things get harder to split into groups the more specific you get, so start with things that are simply and easily observed
      Remember too that a dichotomous key is only as good as the person who made it. These are some of the potential hazards of a dichotomous key:
      1. It relies on a characteristic not present on your specimen (mature bark deeply furrowed when you only have a sapling)
      2. It uses something clear to the author not clear to the user (e.g. too technical of language)
      3. Lack of clear contrast in characteristics (flowers red vs flowers pink)
      4. Uses relative or subjective characteristics (e.g. plants tall)
      5. One group is a clump of multiple characteristics (flowers yellow vs flowers white, red, or absent)
      6. The plant you have is not in the key! Plant ranges have changed over the years and an old manual may say your plant only grows south of Massachusetts. 
      Rather than rewrite a dichotomous key, I wanted to focus in on the attributes of some of the key features used to identify plants by their twigs. A common way to start with our trees is evergreens vs deciduous trees but I skipped that since for now I'm just focusing on hardwoods (synonymous with deciduous and broad-leafed). The next most common way of lumping them is to look at branching patterns. For our broad-leaved trees, branches can be arranged in one of four different ways.

      Witch-hazel (Hamamelis virginiana) bud showing exagerrated zig-zag of alternate branching

      Each node - part of the stem where the buds originate/leaves attach (the internode, the space between two nodes, is nearly absent on spur branches) - only contains one lateral bud.

      Opposite branching in white ash (Fraxinus americana)

      Each node contains a pair of lateral buds.

      Sub-opposite branching in glossy buckthorn (Frangula alnifolia),
       buds are paired, but not directly opposite one another

      Each node contains a pair of buds, though they are not directly opposite one another on the stem. This often will occur on rapid growth of plants that are typically opposite. 

      Catalpa (Catalpa sp.) branch showing two shoots and leaf scar coming out from same node

      Each node contains three or more buds. The least common branching pattern. We only have two species of hardwood trees/shrubs in Vermont with whorled branches. Catalpa and buttonbush.