BIOLOGY 3404F EVOLUTION OF PLANTS Fall 2008

BIOLOGY 3404FEVOLUTION OF PLANTS

Fall 2008Lecture 15

Thursday Nov 13 2008Chapter 18, Living Gymnosperms II:

Coniferophyta

What are conifers?• Con – i – fer = cone-bearing• Most, but not all, produce seeds in cones composed of overlapping scales (modified leaves, or sporophylls), each with one or more often two seeds (matured, fertilized ovules) on the upper side. A few produce fleshy false fruits.

• Most, but not all, have evergreen, needle-like or scale-like leaves. Some are deciduous and others have broad leaves.

• Many have resinous wood; none have vessels.

REPRODUCTION:• As in other gymnosperms, pollen is drawn into the

micropyle and pollen chamber by drying-down of a pollination drop, then the pollen germinates to form a pollen tube which grows to the egg cell of one of two or three archegonia, and a sperm nucleus (non-motile) emerges to fertilize the egg.

• In Pinus, fusion of male and female gametes may be delayed for a year or more after pollination.

• All archegonia are commonly fertilized, but usually only one embryo develops fully.

Reproduction II• A pine seed has "three generations": the seed coat

(integument) is of the parent sporophyte generation (2n), and within this is the megagametophyte generation (female, n) tissue surrounding the embryo (offspring, 2n), which consists of a hypocotyl-root axis, with cotyledons and apical meristem at one end, and another apical meristem and a root cap at the other (bottom).

• The "nuts" of several species of pines are gathered and sold commercially.

Bristle-cone pine, Pinus longaeva, needles in fascicles of five, and young (left) and mature (right) ovulate cones

Pinus radiata microsporangiate cones shedding pollen

Classification (revised on basis of recent

molecular data)Phylum Coniferophyta (= Pinophyta) (5 classes, each with a single order)Class Pinopsida: Order Pinales, family PinaceaeClass Cordaitopsida†: Order CordaitalesClass Voltziopsida†: Order VoltzialesClass Coniferopsida: Order ConiferalesTaxaceae, Cupressaceae, Taxodiaceae, Araucariaceae, Podocarpaceae, Phyllocladaceae, Cephalotaxaceae

[Class Gnetopsida: Order Gnetales]

Pteridophyta

Magnoliophyta

Cycadophyta

Ginkgophyta

Gnetopsida

Pinopsida

C oniferopsida

Coniferophyta

Pteridospermophyta

Cordaitopsid a

Voltziopsida

Class PINOPSIDAOrder Pinales, Family Pinaceae

• 10-12 genera, 250 species• Ectomycorrhizal• Monoecious trees and shrubs with persistent needles (i.e., evergreen, except Larix) on long shoots or short shoots, separate or fascicled, and woody ovulate cones with overlapping spirally-arranged scales, distinct bracts and scales, 2 ovules per scale, and 3 to 18 cotyledons (polycotyledonous).

• The dominant conifers of the northern hemisphere, although also found in the southern hemisphere.

Selected genera of Pinaceae

• Abies (50 species) True firs, including A. balsamea, Balsam Fir

• Cedrus (4) True cedars, natives of Mediterranean Africa • Larix (10-12) Larches, including L. laricina, Tamarack• Picea (50) Spruces, including P. glauca, White Spruce;

P. mariana, Black Spruce; P. abies, Norway Spruce.

Selected genera of Pinaceae II

• Pinus (70-100) Pines, including P. strobus, White Pine; P. resinosa, Red Pine; P. sylvestris, Scots Pine. Bristlecone pines are the oldest living things - at 4,900 years old (see p. 597).

• Pseudotsuga (7) Pseudotsuga menziesii is Douglas Fir of western N. America, widely planted in forestry plantations

• Tsuga (15) Tsuga canadensis is the Eastern Hemlock

Pinus palustris of SE U.S., with needles in bundles (fascicles) of three

Left, Pinus edulis seedling with spirally-arranged single needles (in bundles of two at maturity); Right, Pinus radiata grown from rooted fascicles of needles - the shoot meristem can re-create an entire plant

Abies balsamea

Larix decidua

Class CONIFEROPSIDA,Order Coniferales,Family Cupressaceae

• 18-19 genera, 130 species• Endomycorrhizal• Monoecious or dioecious trees or shrubs with persistent scale-like or awl-shaped leaves and woody ovulate cones (scales fleshy in Juniperus), the bracts and scales fused, arranged oppositely or in whorls, peltate or overlapping, ovules 2 to many per scale, and 2 cotyledons (rarely 5-6).

• Cosmopolitan

Selected genera of Cupressaceae

• Calocedrus (3) C. decurrens is the Californian Incense "Cedar"• Chamaecyparis (7) C. nootkatensis is a common ornamental,

derived from Yellow "Cedar" of the PNW; C. thyoides is the rare and endangered Atlantic White "Cedar"

• Cupressus (15-20) Cypresses (the slender, dark conifers in van Gogh paintings)

• Juniperus (60) Junipers, including J. virginiana, Eastern Red "Cedar"; J. communis, shrubby Common Juniper; many ornamental shrubs.

• Thuja (5) Arbor-vitae, T. occidentalis is the Eastern White "Cedar"

Cupressus goveniana

Juniperus communis

Chamaecyparis obtusa, photo Walter S. Judd, from Judd et al. 2002

Thuja occidentalis, photo Walter S. Judd, from Judd et al. 2002

Order Coniferales, Family Taxodiaceae

• 10 genera, 16 species• Endomycorrhizal• Monoecious trees with persistent or deciduous, linear to

ovate or awl-shaped leaves, globose woody ovulate cones with peltate scales, partially or completely fused with bracts, 2 to 9 ovules per scale and 2 to 9 cotyledons.

• Found in south-eastern and southwestern North America, Tasmania and eastern Asia.

Selected genera of Taxodiaceae

• Cryptomeria (1) Cryptomeria japonica Japanese "Cedar" is commonly cultivated as an ornamental

• Metasequoia (1) M. glyptostroboides is the Dawn Redwood, described as a fossil before it was discovered still growing in China!

• Sequoia (1) S. sempervirens is the Californian Redwood (think ewoks in Star Wars III), grows to about 110 m (367 ft), 2,000 years in age

• Sequoiadendron (1) S. giganteum is the Giant Sequoia, or Bigtree, not as tall as the Redwoods (311 ft), but reach a diameter of 8+ m and 4,000 years.

• Taxodium (3) T. distichum is the Bald Cypress of southern swamps.

Cryptomeria japonica, photo by Walter S. Judd, from Judd et al. 2002

Metasequoia glyptostroboides, the dawn redwood, in China

Fossil of Metasequoia

Sequoia sempervirens, photo by Walter S. Judd, from Judd et al. 2002

Redwoods in coastal California

Sequoiadendron giganteum, the giant sequoia

Taxodium distichum, the bald cypress

Order Coniferales, Family Araucariaceae

• 3 genera, 40 species• Endomycorrhizal except Wollemia which may have

both EM & ECM• Monoecious or dioecious trees with needle-like or

broad leaves, globose ovulate cones with bract and scale fused and ovule 1 per scale, cotyledons 2 or rarely 4

• A Gondwana family found in Australasia and southern S. America

Genera of Araucariaceae

• Araucaria (18) including Monkey Puzzle Tree and Norfolk Island "Pine"

• Agathis (20) Kauri, and Dammar "Pine"

• Wollemia (1) Wollemi "Pine", thought to be extinct for 150 million years before discovered living just outside of Sydney in 1994!

Araucaria heterophylla, Norfolk Island Pine

Agathis australis (photo Christopher Campbell, from Judd et al. 2002)

Wollemi Pine, Wollemia nobilis, in forest near Sydney

Ovulate cone and branch with leaves in four rows

Modern Wollemia and Jurassic Araucaceae fossils

Order Coniferales, Family Podocarpaceae

• 17 genera, ca. 125 species of Gondwana distribution• Endomycorrhizal• Monoecious or dioecious trees or shrubs with leaves of all types: scale-like, needle-like, lanceolate or ovate, terminal, solitary ovules often becoming enclosed by a fleshy aril, or with basal aril.

• Another Gondwana family, mostly in the southern hemisphere, one species in Costa Rica.

Selected genera of Podocarpaceae, plus

families 5-6• Podocarpus (100) Podocarps, including P.

andinus, the Plum-fruited "Yew"• Parasitaxus (1) The only known parasitic

gymnosperm • Family Phyllocladaceae (e.g., Phyllocladus)

Endomycorrhizal• Family Cephalotaxaceae (Cephalotaxus;

Himalayas to Japan) Endomycorrhizal

Podocarpus angustifoliusyoung pollen strobili (KRR)

Podocarpus macrophyllamature ovulate cones (WSJ)

Phyllocladus aspleniifolius, celery-top pine, from Tasmania (left), and P. toatoa in New Zealand (below)

Order Coniferales, Family Taxaceae

• 5 genera, 20 species• Endomycorrhizal• Mostly dioecious trees or shrubs with persistent needle-

like or lanceolate leaves, solitary ovules (ie. not in cones!), when mature more or less covered by a fleshy aril (arises at base of ovule), cotyledons 2

• Northern hemisphere, plus Celebes (Indonesia) and New Caledonia (east of Australia)

Selected genera of Taxaceae

• Taxus (10) the Yews, including T. canadensis, the shrubby Canada Yew, and a lot of garden shrubs

• Torreya (6) includes the California and Florida "Nutmegs"

Taxus, ovules surrounded by fleshy modified sporophylls

Taxus, microsporangiate cones

California nutmeg, Torreya californica, and its fruit

Extinct groups

• Class Cordaitopsida (Extinct): Order Cordaitales (Family Cordaitaceae, Genus Cordaites) ?Mycorrhizae

•  Class Voltziopsida (Extinct): Order Voltziales (e.g., Lebachia) ?Mycorrhizae

Phytosociology of conifers in Canada

• Canada’s forests may be divided into 8 forest regions (Rowe, 1972):

1. The Boreal Forest Region (Taiga) 2. The Subalpine Forest Region 3. The Montane Forest Region 4. The (west) Coast Forest Region 5. The Columbia Forest Region6. The Great Lakes-Saint Lawrence Forest Region 7. The Acadian Forest Region 8. The Deciduous Forest Region

Forest regions are defined by climate and by tree species present

• Five of the eight forest regions of Canada are dominated by conifers, two are mixed forests with both coniferous and deciduous trees, and one small one is predominantly deciduous with scattered conifers. Canada could be called a country of conifers.

• The Boreal Forest Region (Taiga) covers most of Canada, extending to the tree-line, and is predominantly coniferous. White and Black Spruce and Tamarack are widespread, Jack Pine and Balsam Fir are found in the central and eastern areas, and Lodgepole Pine and Alpine Fir are found toward and in the mountains.

Canada’s forests II• The Subalpine Forest Region is basically a taiga of mountain

areas, and is dominated by Engelmann Spruce, Alpine Fir and Lodgepole Pine.

• The Montane Forest Region is a forest of the dry interior of B.C., characterized by the interior form of Douglas Fir, and in the drier south by Ponderosa Pine.

• The (west) Coast Forest Region is a taiga of an extremely humid climate: Western Red Cedar and Western Hemlock dominate, with Sitka Spruce common in the north and Douglas Fir common in the south. Canada's largest trees occur here.

• The Columbia Forest Region, found inland, is similar but less diverse, and the trees smaller.

Canada’s forests III• In central Canada, the Great Lakes-Saint Lawrence

Forest Region is a transition between the boreal taiga and the Carolinian deciduous zone to the south, with hardwoods generally on the better upland soils, and conifers in rocky or sandy exposed sites, along shores and in valleys. Conifer diversity is high, with Red, Eastern White and Jack Pines, Black, and White Spruces (rarely Red), Eastern Hemlock, Eastern White Cedar, Balsam Fir, Tamarack, and Canada Yew.

Canada’s forests IV• The Acadian Forest Region in the Maritimes is similarly a zone of mixed

forest. Red Spruce is common, whereas jack pine and eastern white cedar drop out beyond New Brunswick.

• The Deciduous Forest Region of southern Ontario (also called Carolinian zone; south of a line from Toronto to Goderich) is just that: conifers are outnumbered. Certain pockets have more northerly species; Eastern Hemlock occurs on cool, wet slopes; Eastern White pine is scattered, or with Red Pine on sandy sites; Eastern White Cedar occurs in swamps and on limestone alvars; and Eastern Red Cedar occurs on sandy soils, in barrens, or clearings.

Importance• Economic: HUGE! Timber, pulp & paper• Ecological: HUGE! Conifers form the dominant trees of forests covering large areas of the boreal and subalpine zones; a small diversity of conifers (in Pinopsida) supports (and is supported by) a huge diversity of ectomycorrhizal fungi

• Evolutionary: Largest (in number of species) group of gymnosperms; old enough to provide several great examples of evolution of particular groups corresponding to continental drift