TYPES: PINNATE, PALMATES, PARALLEL; SIMPLE, COMPOUND
May through Oct
lines in a leaf are called veins and function as do our veins
to transport liquids.
Leaf veins occur in three patterns:
PALMATE--like the fingers of your hand come together at your palm, the major veins come together at one point. Example: maple
PINNATE--like a feather, side veins branch off a main vein that runs the length of the leaf. Example: cascara
PARALLEL--main veins run parallel from one end of the leaf to the other. Example: grasses
Tour the Arb, quizzing class with any leaf that strikes your or their fancy as to which type it is.
Question: Which venation pattern is more common?
Students make three columns (or rows) on their paper, one for each venation pattern, and tally each species they encounter in the appropriate column.
concept proved too difficult for students to understand in the
short time allotted for Arb visits.
It needs lots of examples to demonstrate.
leaf is either simple or compound. A simple leaf has the leaf
blade all in one piece.
A compound leaf has the leaf blade ins 2 or more separate pieces (=leaflets).
The hard part is determining exactly what is the leaf. Unless you know what to look for, you could easily think a leaflet is the leaf. A leaf is attached to the stem in a way that leaves a clean break and a distinctive scar on the stem when you break the leaf off. In the angle on the stem above where a leaf attaches you find a bud. It may be tiny, but it is there, ready to develop into new stem if called upon. The leaflet of a leaf attaches to the main vein of the leaf without any discrete scar and with no bud in the angle.
If you have mastered this leaf concept, then you can ask, "Which
is more common, simple or compound?"
"Are compound leaves more often pinnate than palmate?" etc.
The students would make 2 x 2 tables and tally one mark for each species they encounter:
simple | compound
This exercise has right answers, so here are some:
PARALLEL: any grasses, plantain (common weed in the lawn), brodiaeas, Ithuriel's spear (daffodil type leaves), soap plant, iris, false lily-of-the-valley,
PALMATE: currant, gooseberry, vine maple, big leaf maple, thimbleberry, ninebark, coltsfoot, redbud, piggy-back plant, alumroot,
PINNATE: wax myrtle, silk tassel, dogwood, twinberry, coyote brush, willows, alder, Calif. bay, tanoak, osoberry, cascara, azalea, toyon, snowberry, oaks, mock orange, madrone, manzanita, hazelnut, coffeeberry, blue blossom
PALMATE: Calif. buckeye, cow parsnip, lupine, redwood sorrel, blackcap raspberry
PINNATE: red elderberry, angelica, salmonberry, wood rose, Oregon grape.
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