Division: Division: Coniferophyta / Coniferophyta /

Pinophyta IPinophyta I

Coniferophyta / Pinophyta• The conifers are assigned to the

– Division: Pinophyta / Coniferophyta– Class: Pinopsida / Coniferopsida – Order: Pinales / Coniferales

• Termed conifers because most members bear their seeds in cones– Cones protect ovule and seed and

facilitate pollination and dispersal

• They are the largest and most ecologically & economically important of the gymnosperms

Coniferophyta - Uses

– Forest vegetation – Watershed protection– Habitat for variety of animals– Seed as food source esp. for birds &

mammals– Aesthetic appeal– Ornamentals– Paper production– Construction– Resin extraction– Medicinals

Coniferophyta / Pinophyta• The division includes the

– Pines - Spruces– Cedars - Cypresses– Redwoods - Giant sequoias– Junipers - Firs– Hemlocks

• Evolved over 300 mya.

• Present-day genera appeared approx. 170 mya.

• Oldest living and largest trees

Pinus longaeva (Pinaceae) is the oldest known living thing.

Sequoia sp.(Redwoods)

Sequoiadendron sp.

(Giant sequioas)

Sequoiadendron sp.

Coniferophyta / Pinophyta• Widest habitat range

– Sea level– Mountains– Driest deserts– Waterlogged areas– Oceanic islands

Bald Cypress swamp, Bald Cypress swamp, Cupressus sp.Cupressus sp. (Cupressaceae)(Cupressaceae)

Coniferophyta - Families• The conifers constitute 6-7

families, 63 genera & > 600 spp.– Pinaceae (Pines)– Cupressaceae (Cypress family)– Taxaceae (Yew family)– Cephalotaxaceae – Podocarpaceae– Araucariaceae

Family: Coniferaceae/Pinaceae

Family: Coniferaceae/Pinaceae• Strong trees• Emit strong odour from bark &/or

leaves– Resin canals throughout stem & leaves

• Branches whorled or opposite– Consist of long and short shoots

• Simple leaves– Linear / Needle-shaped – Clustered in fascicles of 2-5 needles– Sessile or short petioled on long shoots– Tightly clustered on short shoots– Persistent (evergreen)

Coniferaceae / Pinaceae• Usually have straight trunks with

horizontal branches varying more or less regularly in length from bottom to top, so that the trees are conical in outline

• Members are monecious• Reproduce through micro- &

megasporangiate (staminate and ovulate) cones

• Wood is very hard and pycnoxylic

Pinaceae – Young Stem• Concentric arrangement of

primary tissue• Pith is small• Thick vascular cylinder, comprised

of a ring of separate collateral and open vascular bundles

• Cortex & epidermis relatively thin• Epidermal outline is wavy due to

the presence of scale leaves.

Pinaceae – Older Stem

• The edges of cambia for each VB grow closer and eventually meet complete ring of cambium

• Secondary growth occurs with the laying down of vascular tissue on either side of cambial ring:– Inside: new xylem (secondary xylem)

laid between primary xylem and cambium

– Outside: new phloem (secondary phloem) laid between cambium and primary phloem

needlesneedles

dwarf shoot

branch of unlimited growth/long shoot

thick stem

Pinaceae – Leaf / “Needle”• Adapted for severe environmental

conditions• Epidermis covered by thick cuticle;

epidermal cells thick-walled• Stomata deeply sunken and

amphistomatic• Parenchymatous mesophyll

compact with cell walls having unique infoldings

• Endodermis conspicuous

Pinaceae - Roots• Very similar to angiosperm roots.

– There is an embryonic root which develops into a tap root system from which lateral branching occurs.  

• Mycorrhizae are typically associated with conifer roots and play an important role in seedling growth. 

• The root apical meristem is multicellular with a prominent root cap. 

• The primary tissues are arranged concentrically with diarch – tetrarch xylem at the center, surrounded by phloem, and the pericycle. The endodermis and the rest of the Cortex are typical. The dermal layer, however,  is somewhat ambiguous as the epidermis is indistinct.

Pinaceae - Reproduction• Microsporangiate cones

– Terminally at the stem/branch apex– Spirally arranged, bilaterally symetrical

microsporophylls– Derived from modified branch with modified leaves– Two microsporangia on abaxial surface of the

microsprophyll– Pollen grains bear 2 saccae

• Pollination is by wind

• Pollen grains possess two saccae for extended ‘flight’ and for buoyancy & orientation in the pollination droplet

• Pollination droplet catches pollen

Pinaceae - Reproduction• Each microspore enters a

megaspore via pollen tube

• Reproduction process slow (takes usually 13 months on average to produce a new sporophyte)

Cluster of male coneson apex of

Pinus stem

Pollen (male) cones of Pinus taeda

Microgamete Development in Conifers• First Pathway: In Pinaceae, Podocarpaceae

& Araucariaceae the microspore nucleus divides in the following way:– The microspore nucleus (Androspore) divides

twice by periclinal (parallel to the other surface) walls to cut off two primary Prothallial cells

– The prothallial cells soon degenerate and the large remaining cell is called the Antheridal initial/cell.

– The primary prothalial cells may divide further to form secondary prothallial cells.

– The antheridal initial divides to form a tube cell and a generative cell.

– The generative cell may divide periclinally to form a sterile (stalk cell) and a spermatogenous cell (body cell).

– The spermatagenous cell divides ultimately into two male gametes (or male cells).

Microgamete Development in Conifers

• In other conifers, such as the Taxaceae, Cuppressaceae, Cephalotaxaceae the prothallial cells are not formed & the androspore cell acts directly as an antheridal initial, that is, the prothalial cell and antheridal cell stages are eliminated.

Microgamete Development in Conifers• The pollen grains do not immediately start

germinating on reaching the nucellus.

• In Pinaceae it rests for about a year after the migration of the tube nucleus into the pollen tube (soon after pollination).

• It is during the next spring that the generative cell divides into sterile (stalk) cell and spermatogenous (body) cell, which then migrate into the tube.

• No motile sperm. Pollen tube delivers sperm nuclei into the archegonium

ConiferConifer

PollenPollen

Tube Tube

DevelopmentDevelopment

Pinaceae – Reproduction (cont’d)• Megasporangiate/ovulate cones

– Larger than the male cones– Borne on stem (intercalary)– Spirally arranged, flattened

bract/ovuliferous-scale complex• Woody (ovuliferous) scale (megasporophyll)

envelops the 2 ovules on adaxial surface.• Papery bract / carpellary scale• Micropyles of ovules directed toward the axis of

the cone• Few archegonia/ovule

– Derived from modified branch bearing lateral branches (with seeds) borne in the axils of leaves

AxisAxis of of

conecone

Oviliferous scaleOviliferous scale

nucellusnucellus

integument

integument

Bract scaleBract scale

Female (ovulate) cone on branch of Pinus sp.

maturity

Ovulate (female) cones of Pinus sp.

Pinaceae - Embryogeny• After fertilization the zygote develops. • The zygote divides twice to give four

free nuclei – They are arranged horizontally at the bottom

of the zygote (or it can be said that they migrate to the chalazal end of the archegonium).

– The four nuclei divide once more to form an eight celled structure and

– Arrange themselves in two tiers of four nuclei each.

– The lower one is enclosed by walls all around whereas the upper one is free from walls at their distal end

Pinaceae - Embryogeny• These two tiers divide again to

form a 16 celled proembryo, four tiered structure with four cells each.

• These are from below upwards:– embryonal tier– suspensor tier– rosette tier– Upper/open tier.

Pinaceae - Embryogeny• The cells of the upper tier have no walls

towards their upper side and are also called open cells. Their nuclei slowly degenerate.

• The rosette tier of Pinaceae is unique to this group as usually no rosette tier is formed in the other groups.

• The rosette tier behaves as suspensor tier in other coniferous families.

• The cells of the suspensor tier elongate considerably and push the terminal embryonal cells out of the archegonium and

• Deep into the tissue of the female prothallus, at the expense of which they grow.

Pinaceae - Embryogeny• The four embryonal cells

divide transversely into: – upper four cells that act

as secondary suspensor cells and

– lower four cells.• The primary and secondary

suspensor cells elongate considerably and ultimately split apart longitudinally into four parts each carrying an embryonal cell at its tip.

• As division continues in the embryonal cell, it passes through the quadrant and then an octant stage.

Rosette embryos

Pinaceae - Embryogeny• Each of the octants is a potential

embryo. It is formed from one embryonal cell only.

• There are thus four potential embryos formed from one fertilized egg.

• This feature of embryogeny is termed as cleavage polyembryony which is a characteristic feature of Pinaceae.

• In the course of further development of the potential embryos, one takes the lead and grows more rapidly than the others.

Pinaceae - Embryogeny• The actively growing potential embryo

by cell division, cell growth and differentiation becomes the embryo of the seed while the others die off.

• Only one embryo reaches maturity in one seed.

• Sometimes the cells of the rosette tier also develop into embryos and this is called rosette polyembryony.

• In Pinus, Cedrus, Tsuga and Pseudolarix members of the family Pinaceae, all the four tiers are present: the upper, rosette, embryo & suspensor tiers.

• In Abies, Picea, Larix the rosette tier disappears later.

Pinaceae – Seed Adaptations• The seed has many obvious functional

adaptations• Has winged appendage to aid wind

dispersal (developed from lining of ovuliferous scale).

• The seed is nutritive and is eaten by animals who act as dispersal agents.

• The strong seed coat allows seeds to be dispersed by abiotic agents without damage.

• The seed coat prevents the entry of pathogens and protects it from physical damage.

Pinaceae – Seed Adaptations• The seed contains a mature embryo

which is ready to germinate (endosporic development).– Polycotyledonous: 2-18– Maturing in 2-3 yrs– The megagametophyte is a readily

available food source to the embryo during germination.

• The seed is viable for long periods in the soil. Thus, its germination can be stretched over many years or can be triggered by specific environmental stimuli, like heat.

Mature seed structure

Pinaceae - Germination• Germiation is epigeal

• The first sign of germination is the fracturing of the seed coat and the emergence of the Radicle

• The hypocotyl elongates and lifts the remainder of the seed above the substrate.

• The cotyledons enlarge and absorb nutrients from female gametophyte (now endosperm), further growth of the cotyledons results in their separation from the megagametophyte.

• The cotyledons complete their development and act as photosynthetic leaves.

Pinaceae - Germination• The embryonic shoot (Epicotyl)

emerges and produces the first leafy stem.

• This overtakes the cotyledons as the source of photosynthate.

GerminationGermination

in the in the

conifer conifer

seedseed

Germinating Germinating

conifer conifer

seedseed

Coniferaceae / Pinaceae - Examples• Pinus (Pines)• Picea (Spruce)• Cedrus (Cedars – not WI cedar)• Abies (Firs)

Pinus radiata Pinus palustris

Cedrus sp.

Picea sp.(spruce)