CONIFER EXERCISE the Common Conifers in the Pacific Northwest
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CONIFER EXERCISE The common conifers in the Pacific Northwest belong to the following genera*: Abies, Calocedrus, Xanthocyparis, Juniperus, Larix, Picea, Pinus, Pseudotsuga, Taxus, Thuja, and Tsuga. Most of the common species of these genera are provided in the laboratory. Secure a labeled sample of each of the specimens and, as you examine and study the leafy twigs, answer the questions and fill in the blanks in the following exercise. The materials provided will include most (if not all) of 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) Xanthocyparis nootkatensis (Alaska cedar) – formerly Chamaecyparis nootkatensis Juniperus scopulorum (Juniper) Thuja plicata (Western red cedar) Pinaceae Abies amabilis (Pacific or Amabilis fir) Abies grandis (Grand fir) Abies lasiocarpa (Alpine or Subalpine fir) Abies procera (Noble fir) Larix occidentalis (Western larch) Picea sitchensis (Sitka 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) 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 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 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? _________________ ________________ 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 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 three such species). Of these three species, one has sharp, stiff, and more or less square (in cross-section) leaves. What is the genus and species? ___________________ ___________________ The other two have flat, blunt needles. Note that the leaves of one of these are very white beneath, but green above. Examine these leaves under your 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 ___________________ ___________________ 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 ____________________ ____________________ There are four species with leaf scars as shown in "B", all 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 four 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. Two species, namely ________________ _______________ and ________________ _______________ have stomata on the lower side of the leaves, but not on the upper side (hence the leaves are gray beneath but green above). Of these two species without stomata on the upper surface, one has the needles practically all spreading in a horizontal plane, the upper and lower surfaces of the twigs being similarly exposed, while the other species has the needles on the upper side of the twigs appressed and pointing forward, well covering the top of the twig. On this basis, identify the two species as illustrated below. _______________ ________________ _______________ _______________ The other two species in the same genus (with leaf scars as shown in "B") have stomata on both leaf surfaces. These two species are _______________ _______________ and _______________ _______________. One of these, namely _______________ _______________, has ± straight leaves with one broad central row of stomata on upper leaf surface. The other species, _______________ _______________, has leaves with a sharp curve near the point of attachment to the twig (the leaves of this species resemble hockey sticks). Stomata on upper leaf surface are in two distinct rows with evident green midvein. With a single-edge razor blade, cut very thin leaf cross- sections of all four species and examine under the microscope. Three look like the top sketch, having very small resin ducts just within the lower epidermis; these three species are _______________ _______________, _______________ _______________, and _______________ _______________. The fourth species, _______________ ____________ resembles the lower sketch, in which the resin ducts are much larger and located midway between the midvein and the edge of the leaf and midway between the upper and lower epidermis. 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 ________ _______________.