Early Plants

Characteristics

Psilotum

Lycopodium

Selaginella

Ancient Lycopods

Equisetum

Ferns

Sphenophyta :


Sphenophyta includes the horsetails (branched) and the scourging rushes ( unbranched). There exists only 1 genera now = Equisetum with 15 species, but they were widely represented in the Carboniferous forests.

Equisetum may be the oldest surviving plant genus on earth having evolved approximately 300 MYA

Geographic distribution currently is still widespread with the smaller forms represented ( 3-4ft) thoughout the tropics and and redwood forests, and unevenly through more temperate areas.

Forms standing 15 ft tall may still be found

The sporophyte is pictured here-

what appear to be stiff leaves are actually branches. The leaves (microphylls) are just reduced scales on the stem.

Off of the rhizome you can see adventitious roots.

At the top of the right stem note a strobilus; it is made up of sporangiophores which support sporangia which form the spores.


The strobilus (shown above and below) is generally found at the tip of the plant and is responsible for the
production of spores. The sporangiophores each protect a mess of spore producing sprorangia.

The spores have wings which expand out when dry and aid in dispersal. The wings or elaters are sensitive to humidity- when they hit a moist area they coil up again.

We find the typical life cycle pattern we've seen before, with the gametophyte bisexual and with later maturation of the antheridia relative to the archegonia to prevent self-fertiization.

and the now familiar pattern of zygote forming sporophyte.

Plant morphology: The plant is rather stiff though light- the stem walls have silica in them ( which caused them to be used as scouring pads in colonial times) which increases their rigidity as well ability to grind down herbivore chewing parts.The center and cortex is riddled with air-filled canals which lightens the plant allowing taller growth without heavy lignin investment.

 

Points of Note:

1. Swampy forests of the Carboniferous which existed approximately 300 MYA are the major source of vegetation which eventually became fossilized into the coal and oil sources of today.

Tree forms were approx. 50 ft. in height. The dominant tropical forests made up of these lycophytes and sphenophytes went extict prior to the Permian, as droughts increased in the tropics and glaciers expanded. Only herbaceous members of these two families as well as of the ferns family survived.
However the woody members of the gymnosperms which up to that time were a minor component did survive and greatly speciated in the Permian period. What characteristics of the gymnosperms allowed them to develop drought tolerance?

2. Edible stobili supposedly taste like asparagus.
( this is analogous to the situation of unknown or unusual meat sources which always tastel like 'chicken' supposedly- in the plant world they always taste like asparagus)
You can eat the stems and rhizomes though only after boiling as they are poisonous otherwise ( my questions is why would you consider this in the first place?).

3. They have a number of medicinal uses - as a diuretic for those with urinary/bladder problems:
They have been used in the treatment of TB, gonorrhea: They have been used as an antacid, hair wash for lice, fleas & mites - all these are potent uses- their biochemical products are strong.