COMMON CONIFERS OF THE PNW

Transcription

1 COMMON CONIFERS OF THE PNW The common conifers in the Pacific Northwest belong to the following genera: Abies, Calocedrus, Callitropsis, Juniperus, Larix, Picea, Pinus, Pseudotsuga, Taxus, Thuja, and Tsuga. Most of the common species of these genera are provided in the laboratory. Secure a sample of each of the specimens and, as you examine and study the leafy twigs, compare them to the labeled specimens around the room and answer the questions and fill in the blanks in the following exercise. As you identify your unknowns to species, label them with a piece of masking tape. The materials provided will include the following species, which are classified in the families Cupressaceae, Pinaceae, and Taxaceae. In this exercise, diagnostic vegetative features of the leaves and stem are emphasized first, followed by an examination and comparison of cones (reproductive structures) and by a fill-in key to the common conifers. Cupressaceae Calocedrus decurrens (Incense cedar; does not occur naturally north of Mt. Hood, OR) Callitropsis nootkatensis (Alaska cedar) formerly Chamaecyparis nootkatensis Juniperus occidentalis (Western juniper) Thuja plicata (Western red cedar) Pinaceae Abies grandis (Grand fir) Abies lasiocarpa (Alpine or Subalpine fir) Larix occidentalis (Western larch) Picea sitchensis (Sitka spruce) Picea engelmannii (Engelmann spruce) Pinus contorta (Lodgepole pine) Pinus monticola (Western white pine) Pinus ponderosa (Ponderosa or Yellow pine) Pseudotsuga menziesii (Douglas fir) Tsuga heterophylla (Western hemlock) Tsuga mertensiana (Mountain hemlock) Taxaceae Taxus brevifolia (Pacific yew)

2 VEGETATIVE FEATURES 1. CUPRESSACEAE (Cypress family) Four of the genera have scale-like (as contrasted to needle-like) leaves. These four genera are,,, and. Consider these four specimens only (there is one representative in each genus). One usually will have round twigs (=stems) with 2 scale leaves opposite each other or 3 to 4 scale leaves in a whorl (arising from the same node or part of the stem), while the others appear to have flattened twigs with 2 scale leaves opposite or 4 scale leaves in a whorl. Which species has "round" twigs with the scale leaves in 2's or 3's? Considering the specimens with flattened twigs and with scale leaves in 2's or 4's, identify to species the following sketches of the leaves. Label: The ovulate (=seed) cones of these four genera are distinctive. In general, they are small, often nearly globose or slightly cylindrical, and composed of 2-12 scales (the structures that bear the seeds). The cones of the Cupressaceae are generally smaller than those to be found in the other conifers, especially those in the Pinaceae. Which has a nearly globose, dry cone with the cone scales enlarged and thickest at the end? Which has a usually bluish, often fleshy cone that does not open to shed the seeds? The other two genera have more elongate, dry cones with several scales. The one with only 4 to 6 scales is ; the other with about 10 to 12 scales is Which of these has the larger cones?

3 2. PINACEAE (Pine family) The species in the Pinaceae have needle-like leaves, and usually rather large cones that are composed of numerous, spirally arranged cone scales. Some genera have the needles borne singly along all the twigs, usually in a spiral arrangement, others have the needles borne in small clusters or bundles of 2, 3, or 5 along the twigs, whereas others have the needles borne in terminal tufts at the tips of very short, lateral (spur) branches. Select the four species that have needles in bunches of 2 to 5, or in tufts or spur shoots. Those that have the needles in 2's, 3's, or 5's are in the genus Pinus (pines); the other, which has brush-like tufts of needles at the end of spur shoots, is This is a very distinctive conifer, the only one in the Pacific Northwest that is deciduous (meaning that the leaves are all shed each fall). Note that the branches that we have now (winter) are leafless, but when the leaves flush in the spring, leaves or needles of this tree are young, soft, and obviously freshly grown. Identify the other three species as follows: Needles 2 per bundle Needles 3 per bundle Needles 5 per bundle All the other needle-bearing species have the needles borne singly. Two genera are peculiar in that the leaves are shed rather quickly when the tree (or branches thereof) is cut; therefore, never try to use either of them as a Christmas tree! Both of these genera have evergreen leaves that, when shed, leave a tiny remnant of the leaf-base on the twig; a remnant that can be described as peg-like. In one, the pegs stand out at right angles to the stem and, in the other, they project forward. Separate the two genera with peg-like leaf scars (there are four such species). A B Of these four species, the two species with peg-like leaf bases as in A, have sharp, stiff, and more or less square (in cross-section) leaves. What is the genus?

4 The two species in genus A can be differentiated on (1) the shape of the needles, and (2) the pubescence ( hairyness ) of the young twigs. Of the two species in this genus, which one has somewhat dorsiventrally flattened leaves and no hair on the stems/twigs (glabrous)? (space is provided for you to make a sketch) The other species in this genus, has square leaves in cross-section (not dorsiventrally flattened) and the stems are covered with fine hairs. Which one is this? The two species in genus B have flat, blunt needles. Note that the leaves of one of these are very white beneath, but green above. Examine these leaves under the microscope and note that the whiteness is due to the presence of several rows of white dots (pores or stomata--singular, stoma). The other species is almost the same color on both surfaces (having stomata almost equally numerous on both surfaces). The first species also will have the needles tending to spread in a horizontal plane, in contrast to the other, where the needles tend to spread in all directions. Identify the two species. Needles spreading in one plane, gray beneath, green above, very unequal in length: Needles spreading in all directions, about the same color on both surfaces, not markedly different in length:

5 Now you should have left only the species of Pseudotsuga and Abies, all of which have comparatively smooth twigs where the needles have been shed. Examine the leaf scars carefully. Some scars are nearly circular, or slightly elongate (with reference to the axis of the branch), whereas at least one of the species has the scars broader than long and somewhat crater-like or umbilicate (navel-like). Recognize the genera as represented in the following two sketches. (This is not a hard and sharp distinction, and does not always "work".) Genus Genus "A" has pointed and almost sharp buds, in contrast to those of "B", which are more blunt. "A" tends to have less regular opposite branching than does "B". What is species "A"? Cheer up, if you cannot recognize it from the leaves, you surely can from the cones, as they are perhaps the most distinctive cones found among our conifers, having a 3- cornered bract extending past each seed-bearing scale. To repeat, the species is

6 There are two species with leaf scars as shown in "B", both in the genus. The species of this genus usually cannot be distinguished by the cones, since a peculiarity of this genus is that the cones are never shed in their entirety, but only scale by scale, leaving the axis of the cone on the tree, standing stiffly erect. These two species can be distinguished, though, by the presence of stomates on one or two surfaces, by differences in the arrangement and attachment of leaves, and by differences in positioning of resin ducts in the leaves. One species, namely _ has stomata on the lower side of the leaves, but not on the upper side (hence the leaves are gray beneath but green above). In addition, this species without stomata on the upper surface has the needles practically all spreading in a horizontal plane, the upper and lower surfaces of the twigs being similarly exposed. On this basis, identify the species as illustrated below. To repeat, this species is The other species in the same genus (with leaf scars as shown in "B") has stomata on both leaf surfaces, and ± straight leaves with one broad central row of stomata on its upper leaf surface. This species is:

7 As with the scale-leaved species, many of the needle-leaved conifers can be recognized by their cones alone. Consider the following features: Two genera have cones with a 3-pointed bract arising from beneath each cone scale; the bracts may be about as long as the cone scales (barely visible) or considerably longer than the cone scales. Which of these has the larger cone? and which the smaller?. Two cones have sharp hooks or spines near the tip of the scales. One of these has somewhat lopsided, smaller cones; it is. The other has a much larger, symmetrical cone; it is. The third species in this genus has the largest (or at least the longest) cones of our native conifers; it is. Of the three genera--abies, Tsuga and Picea--the species of Abies do not shed their cones as a whole, and we shall make no attempt to distinguish between them in this exercise. Our species of Picea and Tsuga have smaller, somewhat woody cones that range in length from about 1 inch (2.5 cm) in Tsuga heterophylla, to 1-2 1/4 inches (3-6 cm) in Tsuga mertensiana, to 2 1/4-4 inches (6-10 cm) in Picea.

8 3. TAXACEAE (Yew family) The species in this family are characterized by the lack of woody cones; the seeds are borne singly and are surrounded by a fleshy, reddish, berry-like aril. The one native species in this family is a shrub or small tree of the forest understory. The leaves are flat, pointed, and arranged in two rows (two-ranked) on the branches and abruptly tapered to a short, petiole-like, decurrent base. What is the genus and species?

9 KEY TO COMMON CONIFERS To summarize your study of the conifers, fill in the blanks in the following key with the proper generic and specific names. Start with the first couplet (1a and 1b). Read both leads before making a decision regarding which of the two to follow. After making a decision, proceed in like manner through the rest of the key. You are expected to recognize these species of conifers by the twigs as well as by the cones. 1a. Leaves deciduous each fall, borne in tufts of on short lateral (spur) shoots; cones with 3-cornered bracts visible between the scales 1b. Leaves persistent from year to year, not borne in tufts on short lateral shoots; cones (with one exception) without visible 3-cornered bracts 2a. Leaves scale-like 3a. Twigs usually round; cones fleshy, globose, usually bluish, the cone scales not separating when the seeds mature 3b. Twigs flattened; cones dry, globose or slightly cylindrical, not bluish, the cone scales separating when the seeds mature 4a. Cones globose; cone scales thickened and knob-like at the tips 4b. Cones cylindrical or slightly so; cone scales not thickened at the ends 2b. Leaves needle-like 5a. Cones with scales; leaves obviously in pairs along the twigs, the tips of the dorsal and ventral pair of leaves at a different level than the tips of the lateral pair of leaves 5b. Cones with 4-6 scales; leaves apparently in whorls or 4, the dorsal and ventral pair of leaves about the same length as the lateral pair of leaves 6a. Needles in fascicles of 2, 3, or 5 7a. Needles 5 per fascicle 7b. Needles 2-3 per fascicle

10 8a. Fascicles containing 2 needles 8b. Fascicles containing 3 needles 6b. Needles borne singly, not in fascicles 9a. Leaf scars raised, the twigs roughened by the peg-like projections 10a. Needles mostly square, sharp, and stiff 11a. Twigs glabrous, needles dorsiventrally flattened 11b. Twigs pubescent with fine hairs, needles not dorsiventrally flattened 10b. Needles flat, blunt, and pliable 12a. Needles much more whitish on the lower surface than on the upper, tending to spread in one plane, very unequal in length 12b. Needles almost the same color on the two surfaces, tending to spread in all directions except perhaps on the lower surface of the twig, not markedly different in length 9b. Leaf scars not raised, either smooth or umbilicate (navel-like) or leaf scars hidden by the decurrent leaf bases 13a. Leaf bases decurrent; leaves mucronate at the apex; seeds borne singly, surrounded by a fleshy aril 13b. Leaf bases not decurrent; leaves obtuse to rounded at the apex; seeds borne in woody cones 14a. Needle scars broader than long (with reference to the axis of the twigs); buds pointed; branches alternate or opposite 14b. Needle scars usually at least as long as broad; buds blunt; branches regularly opposite

11 15a. Needles without stomata on the upper surface, nearly all spreading in a horizontal plane, the upper surface of the twig (as well as the lower) not concealed by needles 15b. Needles with stomata (and thus whitish) on both surfaces, leaves +/- straight with 1 broad central row of stomata on upper surface