The Coniferophyta is a relatively large
group of plants which forms the dominant component of vast ecosystems, especially in the northern hemisphere (Northern Boreal Forest). Some of these plants are the largest organisms on the planet and also have the greatest longevity. This taxon is represented in the Southerh Hemisphere as well, especially in New Zealand.

The most significant vegetative adaptations of this taxon include Secondary Growth and the production of protective Buds.

They also have a significant amount of internodal elongation which allows them to grow faster than the other plants we have reviewed.

Their Leaves have a battery of adaptations which foster survival in extreme habitats. Many of these traits are "Xeromorphic".

The "tree line" in the northern hemisphere is the conifer line as these are the most tolerant woody plants with regard to heat, cold, aridity and combinations thereof.

Link to Secondary Growth

Secondary Growth is the result of Lateral Meristems (Vascular Cambium & Cork Cambium). The word Cambium signifies the meristematic nature of these two.

The plane of cell division in both is predominately Periclinal (parallel to the surface). This produces radial files of cells which increase the girth of the organ in which they occur.

There are also some Anticlinal (Perpendicular to the Surface) cell divisions which increase the circumference of Lateral Meristems. This is necessary to compensate for the increased girth caused by increases in secondary vascular tissues and cork. Otherwise, secondary growth would produce interrupted sectors with deep cracks (little secondary growth) and elevated areas (lots of secondary growth).

The Vascular Cambium is a continuation of the Procambium. However, it induces cambial activity in adjacent cells and thus further adds to its circumference.

The Cork Cambium arises de novo (new) from Parenchyma cells.

The Vascular Cambium produces
Secondary Xylem (wood) and
Secondary Phloem (inner bark).

Secondary Xylem provides structural support but it also provides a conduit for the transport of water throughout the entire plant.

It also provides a water reservoir! Water can accumulate in the "heartwood" so that it becomes available for transport in the "sapwood" if there is insufficient water coming from the roots.

The largest conifers are several hundred feet high and their root systems are equally large if not of greater extent.

The Tracheary Elements in conifers are
Tracheids. These serve the dual functions of the secondary xylem but they represent a compromise in terms of both.

Tracheid properties differ depending on the environmental conditions under which they are formed.

Tracheids have a thicker wall and a narrower diameter if they are formed during periods of water or temperature stress. The opposite occurs during times of plenty.

The former tracheids are better for support.

The latter tracheids are better for conduction.

Angiosperms produce Vessel Members and Fibers in their Secondary Xylem. These are more specialized for conduction or support, respectively, and are, thus, more efficient at both.

Secondary Phloem transports sucrose
throughout the organism. Its Sieve Elements in the Coniferophyta are Sieve Cells. These have Sieve Pores in their walls. They are lined with Callose and they are  similar to sieve cells in seedless vascular plants.

Angiosperms have Sieve Tube Members which are more efficient for conduction.

The Cork Cambium (Phellogen) produces Cork (Phellem). Cork is commonly known as "outer bark". This tissue is dead, except for the Phellogen and its immediate derivatives. The walls of Cork Cells are impregnated with Suberin. This is a hydrophobic material that is water-proof and pathogen-proof.

It prevents excess water loss and it also insulates living cells from the external environment. Some plants like Douglas Fir and Ponderosa Pine have barks which protect them from prairie fires. This allows them to survive in environments which are hostile to their competitors.

The Apical Meristems of Conifers are multicellular. They have much in common with the apical meristems of flowering plants. They do not have noticeable "Initials".

The Shoot Apical Meristem has a prominent Quiescent Center which has been called the Central Mother Cell Zone.

The Root Apical Meristem tends to be broad and all of the tissues of the Root Body and Root Cap are produced by the same Meristem Proper.

Conifer Leaves have many adaptations that equip them to deal with dry, hot and cold environments.

They have a reduced Lamina (blade).

Pinus monophylla has a cylindrical shape. This give it a small Surface Area/Volume ratio. This means that evaporation will be minimized compared to a flat blade.

If the separate needles of 2-5 needle Pines are viewed together they form a cylinder.

The Epidermis has a thick Cuticle & its walls may be Lignified.

Stomata are "sunken".

A Sclerified Hypodermis (layer(s) below Epidermis) is usually present.

Closely spaced Chlorenchyma reduces the wall area available for evaporation.

An Endodermis separates the  Mesophyll & Vascular Bundle.This must provide better regulation of water movement between the Vascular System and the Mesophyll.

The Vascular Tissues are unbranched and reside in the center of the leaf. This would help to limit evaporation as well.

Stems

All Conifers produce Periderm. Periderm usually arises in the subepidermal Parenchyma. Several cells divide Periclinally and continue to divide this way. This results in radial files of cells which emanate from these Meristematic Cells which are called the Cork Cambium or Phellogen. The Phellogen tends to produce cells towards the outside of the Stem or Root. Meristematic activity spreads laterally until the entire circumference of the organ is encompassed. Cork Cells (Phellem) have Suberized walls and are dead at maturity. Suberin is waxy and prevents excess evaporation. It is almost indigestible by microbes and thus provides a barrier against pathogens. The absence of protoplasm in the dead cork cells deprives pathogens of any nutrients. It also insures that there are no Symplastic connections through which viruses might spread. Commercial Cork comes from the "Cork Oak". It has insulating properties because air is trapped within the individual cork cells. Consequently, the Periderm has insulating properties which lend some protection against temperature extremes in nature. The Periderm is an extremely important adaptation.

The Primary Root of Conifers is similar to what we have seen before. However, Conifer Roots have Secondary Growth. They have Secondary Vascular Tissues and Periderm. This allows them to expand over time and thus increase their ability to anchor the ever-increasing above ground biomass of the shoot system. It also allows them to persist for centuries in some cases. The Periderm has functions similar to the Periderm on aerial structures. Secondary Vascular Tissues also have the same primary functions as their aerial counterparts.