Conifers
Cone-bearing gymnosperms adapted to cold
The conifers are cone-bearing gymnosperms that are most frequently evergreen trees, but some are deciduous (e.g. Taxodium). Conifers dominate in taiga biomes, as well as temperate areas with poor soils. Most polar, and many temperate, conifers have a pyramid shape with weak branches: an adaptation to shed snow. In addition, conifers have many adaptations to survive in cold, dry conditions: needle-like leaves, hypodermis in leaves, sunken stomata, narrow xylem cells, and resin canals to name some. Conifer evergreens are sometimes referred to as "softwoods" because they have wood that is light-weight, weak in shear (along the grains), but strong in tension. It is usually light in color and cheaper, therefore used for building inexpensive furniture or used for paper pulp. The conifers include some of the most extreme organism on Earth: the tallest organisms (i.e. Sequoia sempervirens), the heaviest (non-clonal) organisms (i.e. Sequoiadendron giganteum), the oldest (non-clonal) organism (i.e. Pinus longaeva), and the widest (non-clonal) plants on Earth (i.e. Taxodium mucronatum).
Biology
Stems
Usually trees or shrub-like trees
Eustele with bifacial cambium; Pycnoxylic wood
All living conifers are woody, but Aethophyllum stipulare , was a herbaceous conifer, from the Middle Triassic that grew up to 2 meters in height
Leaves
Needles, scale-like, awl-shaped leaves in most conifer species
Some tropical conifer species have elliptical, linear, broader lanceolate, ovate, or nearly elliptic leaves (e.g. Agathis, Podocarpus)
Veins are usually parallel
Plants are mostly evergreen and adapted to withstanding cooler weather
These leaves have xeric adaptations such as sunken stomata and a hypodermis
A few deciduous conifer taxa exist in wetlands (e.g. Taxodium, Metasequoia, Larix)
Reproductive Structures
Mostly monoecious plants
Differentiated megasporangia (♀) and microsporangia (♂)
Female ♀ cones (megasporangiate cones)
Large, woody cones
Compound structure (main axis with branches called scales)
Ovules attached to scale in various orientations
Woody scales subtended by leafy bract
Male ♂ cones (microsporangiate cones)
Small in size; not woody
Simple structure (main axis with leaves)
Geologic Age
Pennsylvanian - present
Appear in Late Carboniferous: Swillingtonia denticulata (Scott & Chaloner 1983)
Remained dominant through most of the Mesozoic
Classification
└Pinales: pine-like conifers (below)
Diversity
Extant taxa: 66 genera, 589 species
Conifers have the largest diversity of living gymnosperms
7 extant families:
Cupressaceae
Cypresses, Redwoods
Actinostrobus,
Athrotaxis,
Austrocedrus,
Callitris,
Callitropsis,
Calocedrus,
Chamaecyparis,
Cryptomeria,
Cunninghamia,
Cupressus,
Diselma,
Fitzroya
Fokienia
Glyptostrobus
Juniperus,
Libocedrus,
Metasequoia,
Microbiota,
Neocallitropsis,
Papuacedrus,
Platycladus,
Pilgerodendron,
Sequoia,
Sequoiadendron,
Taiwania,
Taxodium,
Tetraclinis,
Thuja,
Thujopsis,
Widdringtonia
Also called Cheirolepidiaceae
Group resembling Cupressaceae with distinctive pollen type (Classopolis)
Possibly insect-pollinated and adapted to semi-arid environments
The "frenelopsids" are a group of Cheirolepidiaceae with jointed stems, thick internode cuticles, sheathing leaf bases and reduced free leaf tips. The leaf morphology has been noted as being similar to that of halophyte Salicornia. Several members of the family appear to have been adapted for semi-arid and coastal settings, with a high tolerance of saline conditions.[1]
Palissyaceae †
Palissya †
Late Triassic-Early Cretaceous of Laurasia and Eastern Gondwana
Stachyotaxus †
Late Triassic of the Northern Hemisphere
? Knezourocarpon †
Jurassic of Australia
Above: Reconstruction of Palissya (From Pattemore et al. 2014)
Additional Reading
