Morphology

Morphology and Anatomy

Literature: An excellent scientific review about Pinaceae in relation to all other conifers is found in Price RA. 1989. J. Arnold Arb. 70(2): 247-305. Part one.

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PLANT: The conifers are trees (or rarely shrubs) usually monopodial.

WOOD: The secondary xylem is very uniform, it consists mainly of tracheids and is called softwood (contrary to hardwood from the Angiosperm trees), and it contains resin, which is often situated in cells.

SHOOTS: Most conifers are monopodial trees, which implies that the main part of the new shoots develop close to the ends of the existing shoots. The shoots are often situated in whorls around the central axis, especially on the young plants. The shoots are not always of the same length, but marked dimorphism is only found within some genera of Pinaceae and Sciadopitys. The shoots of Pinaceae lignify and change color rather quick in relation to the shoots of most other conifers among which Sciadopitys is one of the fastest to lignify.

Cedrus, Pseudolarix and Larix have a special sort of dwarf shoots similar to each other. From the meristem by the needles of as well long shoots as dwarf shoots these three genera are able to grow either a new long shoot or a new dwarf shoot making 4 combinations, the 3 of which is seen on the photo: Larix: Click here , where long shoots from both long and dwarf shoots as well as dwarf shoots from long shoots are shown. The most common: a dwarf shoot from an earlier dwarf shoot is most easily seen on Cedrus because it is evergreen. — Cathaya seems to develop some shoots most similar to long shoots and other shoots most similar to dwarf shoots, but not quite as evident and regularly as by Cedrus/Pseudolarix/Larix, and it is a question whether true shoot dimorphism exists within Cathaya.

Pinus has a quite different form of dwarf shoots, which is seen on the photo: Pinus: Click here . The branch at the left is a long shoot from last year with many dwarf shoots each of which has a bundle containing two needles. The almost vertical new long shoot, which is seen at the right is created from the meristem situated on the needle end of one of the former dwarf shoots from last year. The new long shoot is covered with scale leaves, which fall of within short, but new dwarf shoots with future needles are growing from the base of the scale leaves now. No meristem is left directly on the old long shoots, and the shoots of next year will all start from the meristems just under the needles.

Sciadopitys, which forms its own family Sciadopityaceae, is quite different. The shoots of Sciadopitys are always long shoots (but of very different length from 2mm to 30 cm) covered with scale leaves and each long shoot ending in a verticil ("umbrella") of special double needles. The verticils of Sciadopitys may be interpreted as dwarf shoots, but they are most likely analogous and not homologous to the different dwarf shoots from Pinaceae. All the new shoots of Sciadopitys are created from the meristems by the double-needles of the verticils as seen on the photo: Sciadopitys: Click here, whereas no shoots are formed directly from the long shoots, although it may falsely look so. On the photo five new shoots created from five independent buds are seen, but, as seen too, some of the shoots are at first fused together with each other and afterwards they separate after some time in such a way that later it wrongly looks like the one of them has grown directly from somewhere in the middle of the other, which now looks like an ordinary long shoot, but that is not the truth. — New shoots may develop even from older verticils, a new shoot from a 10 years old verticil has been observed.

LEAVES: The conifers are with a few exceptions evergreen. The first leaves that develop on the seedlings after the cotyledons are needlelike and spirally arranged by all conifers regardless of the appearance of the later leaves. See the photo: Cupressaceae_seedling: Click here. Even the genus phyllocadus, where the green leaves are replaced by phylloclades (green flattened shoots) on the grown-up plant, has ordinarily needles on the seedlings. Most conifer leaves have one vascular bundle, and all conifer leaves except the Taxus-clade (Taxus, Pseudotaxus and posibly Austrotaxus) contain resin canals.

Pinaceae: Larix and Pseudolarix are deciduous, all other genera are evergreen. All the green leaves are often flattened, needle-shaped leaves called needles. The needles of most genera have a more or less marked midrib with a band of stomata on each side, and each needle has one vascular bundle except for Pinus diploxylon (subgenus Pinus), which has two. The needles of the long shoots are spirally arranged and so are the scale leaves of Pinus. The arrangement on the dwarf shoots of the needles of Cedrus/Pseudolarix/Larix is usually mentioned pseudowhorls, whereas the arrangement of the needles of the very short shoots of Cathaya are still spirally arranged. The needles of Pinus are arranged in one bundle on each dwarf shoot, each bundle containing 1-8 needles (usually 2, 3 or 5).

Araucariaceae: All the leaves in this family have contrary to most other conifers more than one vascular bundle. The leaves of the genus Araucaria are triangular-lanceolate or awl-shaped, sessile, crowded, and spirally-arranged, whereas the leaves of the genus Agathis (incl. Wollemia) are widely spaced, ovate-lanceolate to elliptic, well-spaced petiolate, spirally-arranged to almost opposite (maybe on the same tree). Shoot of Agathis dammara see photo: Agathis: Click here.

Podocarpaceae s.l.: This is a very comprehensive and very variable family. As mentioned before, the genus Phyllocladus has not even green leaves on the grown-up plant. The leaves from the genus Nageia have more than one vascular bundle and may be rather ovate-lanceolate , whereas the leaves from all the other genera only have one vascular bundle, and leaves of many genera are linear-lanceolate to linear-eliptic, some of which can be rather big. Leaves of some species of the genus Podocarpus are so similar to the leaves of Taxus that Feustel (1929) believed that they belonged to the same family. On the other hand, some other genera within Podocarpaceae have developed green scale leaves much like the ones, which are found in Cupressaceae.

Sciadopitys: There is still no obvious explanation of the nature of the long, double-needles of the Sciadopitys, which each contains two vascular bundles.

Taxaceae s.l.: Each needle has one central vascular bundle, underneath surrounded by a band of stomata to each side. The needles are spirally-arranged, but they are often situated in two rows. For instance in Cephalotaxus some of the needles may look nearly opposite.

Cupressaceae s.l.: The leaves have one vascular bundle. The shape of the leaves varies from flat needles by Cunninghamia, Sequoia, Metasequoia, Taxodium, and Glyptostrobus, awl-shaped needles by Cryptomeria, young Taiwania, and some Athrotaxis, whereas scale-leaves dominates by grown-up Taiwania, Sequoiadendron, some Athrotaxis, and by most adult Cupressaceae s.s. The arrangement of the needles varies from spirally to decussate arranged, even in whorls of three on some Juniperus. Dimorphism of the leaves exist very wide spread in the family. In many genera both the juvenile needle and the grown-up scale form exist, in some species they even exist simultaneously. Example of needle dimorphism by Juniperus see photo: Dimorphism: Click here. — Metasequoia, Taxodium and Glyptostrobus are annual deciduous (preferably it is the outermost part of the shoots that drops).