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30 Cards in this Set

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Classify SELAGINELLA
D- Eukarya
K- Plantae
P- Tracheophyta
C- Lycopsida
O- Selaginellales
F- Selaginellaceae
G- Selaginella
What are some defining characteristics of SELAGINELLA?
-AKA LITTLE CLUBMOSS or the SPIKE MOSS
-best developed in tropical and subtropical regions
Discuss the GENERAL MORPHOLOGY of SELAGINELLA.
-relatively small plants, but some vine like climbers are reported to achieve lengths of 20ft or more
-mostly perennial plants (live on from year to year)
-some spp which live in regions of alternating favourable and unfavourable climatic condiions can withstnad remarkable severe environments
-has 4 growth habits (another FC)
-branching of the shoot system is of the terminal type with a strong endency to pseudomonopodial developement in most spp, some show dichotomous
What are the 4 GROWTH HABITS of SELAGINELLA?
1)Prostrate or Creeping
-mat forming

2)Upright or Ascending
-supported by prop roots

3)Scramling or Climbing
-vine like

4)Rhizomatous
-dorsiventral, frond like aeiral shoots arise from underground rhizomes
Discuss the LEAF MORPHOLOGY of SELAGINELLA.
-microphylls
-leaves are always small (few mm) and they are served by a single leaf trace
-each leaf bears a small tongue like structure called a LIGULE on its upper or adaxial surface, near the base. May secrete water or mucilage which serves to keep the apical bud moist

Two distinctive patterns:
1)ISOPHYLLOUS:
-all leaves are approx the same size
-phyllotaxy is helical
-mostly occur in relatively dry areas
-survive well in dry environments
-these are the plants that return from a yellowish death to a green (ie: Resurrection Plant)

2)ANISOPHYLLOUS
-leaves are arranged in 4 rows along the stem, 2 lateral rows of larger leaves and 2 dorsal rows of smaller leaves
-the result is a shoot that is dorsiventral and has a bilateral symmetry
-phyllotaxy is still helical and the anisophyllous pattern is superimposed on it
Discuss the ROOT MORPHOLOGY of SELAGINELLA.
-has a primary root which develops in the emryo
-major roots are adventitious
-roots arise from the stem at angles of branching, and thee may be one or two at each angle
-if there are two, one is dorsally placed and the other ventraly on the dorsiventral shoot
-in the rhixomatous spp, roots arise oly on the underground axis
-in the creeping forms, they arise at branchings all along the shoot and are relatively short
-in the ascending and vine like spp, they arise from the lower branchings of the shoot and descend to the ground like prop roots, usually not branching until the reach the soil or just before
-branch terminally, either equally or unequally
What are ANGLE MERISTEMS?
-meristems which give rise to roots in Selaginella
-roots arise from tiny meristems in the angles at the surface, not internally, and at the beginning lack a root cap
-they are actually branches of the shoot apex and the roots thus seem to be equivalent to shoot branches (can also form shoots if conditions are right)
What is a RHIZOPHORE?
-term used by some botanists to describe the branches of the shoot system which ultimately are transformed into typical roots
-not a very useful term, just realize that there is no sharp distinction between shoots and roots in plants like Selaginella
Discuss the SHOOT and ROOT ANATOMY of SELAGINELLA.
-3 tissue systems are well defined
-stele is basically an EXARCH PROTOSTELE
-some spp have SIPHONOSTELE
-stele can vary with different parts of the plant
-stele in Selaginella can be broken into 2 or several protostele (each called a MERISTELE), each with its own endodermis
-if like this, called POLYSTELIC
-leaves are MICROPHYLLS
-stele is often suspended in a cavity/lacuna by elongated cells or chains of cells called TRABECULAE
-branching is terminal

-anatomy of the root is very similar to the stem except that in general, it is impler
-roots are often centrarch
-polystele does not occur
-no leaf traces... of course
-central lacuna around the stele and the trabeculae may or may not be present
-root resembles a shoot apex early on except for the absence of leaf primordia
-later begins to form a root cap by the inroduction of another plane of division in the apical cell or group of apical initials
-it then becomes a typical root
What are 2 interesting features of Selaginella?
1)Stele is often suspended in a cavity or lacuna by elongate cells or chains of cells called TRABECULAE

2) All isophyllous spp of dry habitats have true vessels
Discuss the APICAL MERISTEM ANATOMY of SELAGINELLA.
-shoot apex has a distinct apical cell situated in the centre of a surface layer of elongated cells, in some cases, the apical cell is replaced by a group of initials
-root apex is rather similar, but the promeristem itself is covered by a root cap
-where an apical cell is present, it can be sen that this cell cuts off derivatives from the base of the pyramid in additnoi to those cut off from its lateral, sloping faces as in the shoot
Discuss the SPOROPHYTE of SELAGINELLA.
-since Selaginella is a LYCOPSID, we find sporangia produced adaxially upon sporophylls
-leaf traces run into sporophylls but not into the sporangia

HETEROSPORY condition (ie: 2 sizes of spores)
1) Megaspores: from a megasporangium, contains only four megaspores which germinate into a female gametophyte
2) Microspores: from a microsporangium, produces a large numbre of spores
Discuss the GAMETOPHYTE of SELAGINELLA.
-microspore makes the male gametophyte
-megaspore makes the female gametophyte
-both gametophytes are reduced in the extent of their development and for the most part, remain within the spore wall or emerge only slightly (ENDOSPORAL)
-therefore, the gametophytes are dependent upon food reserves stored in the spores

Male Gametophyte
-begins to develop ordinarily before the microspore is shed
-except for one small cell (PROTHALLIAL CELL), the gametophyte consists solely of an ANTHERIDIUM, a sterile jacket surrounding a number of BI-FLAGELLATE sperm
-spores are shed during the process of gametophyte development, which is completed on the ground
-spore wall then cracks open and the swimming sperms that are released require water to swim to the archegonia

Female Gametophytes
-first development is one where the nucleus divides repeatedly without associated wall formation so that a multiculeated protoplast results (FREE NUCLEAR DIVISION)
-followed by wall formation which begins in the region under the tri radiate mark and spreads through the rest of the protoplasmic body. The completion of cell wall formation may be long delayed
-upper cellular portion of the gametophyte continues to grow after wall formation, the spore cracks along the triradiate mark, and the gametophyte protrudes to some extent
-the protruding portion forms rhizoids and archegonia which are thus exposed and available for fertilization

**embryo emerges as a free living sporophyte after a period of nature in the archegonium. There is both a SUSPENSOR and a FOOT in the embryo**
What is the significance of HETEROSPORY?
-ensures cross fertilization since self fertilization is impossible
-even if they did incest it up (ie: from same parent sporophyte), there will be some genetic difference

-in the life cycles of various vascular plants, heterospory is regularly associated with endosporal gametophytes, although they are two quite different things
-it ought to be possible to have endosporal gametophytes associated with homospory, but this has never been found
-endosporal gametophyte introduces a system in which the gametophyte is provided with all necessary nutrients for its development within the spore from which it develops
-endosporal gametophyte introduces a system in which the gametophyte is provided with all the necessary nutrients for its development within the spore from which it develops, but still requires external water for developement and fertilization
-separates the sexes and assigns attributes accordingly (ie: larger female because needs more nutrients)
How often do SELAGINELLA sexually reproduce?
-more often than Lycopodium
-apparently, a female gametophyte will not give rise to sporelings until the presence of sperm triggers them too.
What is a FORM GENUS?
-a genus which is set up to include a particular kind of plant part
-when a whole plant is finally put together, the name taken for he organism is the form genus name which was first applied to some part of the plant

Eg's
-Stigmaria is given to the anchorin organs found at the base of a Lepidodendron tree
What are some defining characteristics to the Group Protolepidodendrales?
-fossil spp
-bear a strong resemblance to modern Lycopodium
-tended to be somewhat larger though
-upright axes arose from horizontal rhizomes and the stems were clothed with simple leaves, each served by a single leaf trace which extended into the leaf
-leaves were sometimes dichotomously branched one or more times
-the stele in the stem was EXARCH PROTOSTELE
-sporangia were lateral in position but rather than being scattered among th eleaves, they were regularly associated with the leaves
-homosporous
-stems up to 2.5cm in diameter and leaves 3cm long which branched in 3's near the tip
-believed to be the ancestral stock which, itself was derived from the Zosterophyllopsida, gave rise to the major lycopsid evolutionary lines
What are some defining characteristics to the Group LEPIDODENDRALES?
-2 Genera of interest: Lepidodendron & Sigillaria
-group began before the Devonian
-both genera widely distributed geographically
Discuss the MORPHOLOGY of LEPIDODENDRON
-AKA the scale tree
-45m high, 1.2-1.8m wide
-stems were densely clothe dwith leaves, but these fell after a time, leaving behind elevated 'LEAF CUSHIONS' (base of leaves)

Leaf Cushions:
-cushions are the scales and hence the name
-leaf cushions are roughly diamond shaped
-leaf scar approx 1/3 from the top, left when the leaf dropped away
-just above is the LIGULE
-PARICHNOS SCARS flank the scar of the leaf trace, represent channels of loose parenchymatous tissue which connected the mesophyll of the leaf with the inner tissues of the stem and presumably served to provide aeration

Leaves:
-the portion that extended beyond the cushion were about few mm to >1m in length

Roots:
-base of the turnk was a double dichotomy which resulted in 4, large horizontally spreading structures which extended out from the trunk and dichotomized repeatedly
-these root like organs are often found isolated and are assigned to the form genus Stigmaria
-major branches were covered with small lateral roots up to 35cm in length, branched dichotomously
-when these rootlets separated or died, they left scars which appear as small pits (STIGMA)
Discuss the ANATOMY of LEPIDODENDRON
General:
-stele was PROTOSTELE or SIPHONOSTELE, considerable variability in different parts of the same plant
-MICROPHYLLOUS
-has an active VASCULAR CAMBIUM which only produces a small of secondary xylem inwards
-CORK CAMBIUM produced PERIDERM
-pereiderm was produced both to the inside and the outside of the meristem, but apparently mostly to the inside
-the leaf cushions outside it persisted for ome time, which is one reason for thinking that it may have been a living tisue, but they ultimately were sloughed off
-periderm became veryh thick and was the main support for the tree because the secondary xylem was of such limited extent

Roots:
-appendages (or root proper) formed a connection with the primary xylem of the axis which was maintained even after secondary tissues were formed
-stele is a simple protostele without secondary tissues
-it is surounded by an inner layer of cortex
-there is an outer layer of cortex, but the area between the cortical layersis an air space which seems to be natural and not the result of decay
-stele and inner cortex are joined to the outer cortex by a strip of parenchyma
-believed that there were no root hairs
-roots can be considered to be modified leaves, or possibly distinctive enations which evolved in parallel to leaves
Discuss the REPRODUCTIVE STRUCTURES of LEPIDODENDRIDS
-produced cones that vary up to 30cm long
-cones either terminated the ultimate branches of the shoot or arose as special side branches
-they consisted of helically arranged ligulate sporophylls which turned upward beyond the attachment of the sporangia and overlapped the sporophylls above
-the sporangia were borne singly on the adaxial surface of te sporophylls and, as in the other lycopods, received no direct vascular supply from the sporophyll trace
-isolated cones are called LEPIDOSTROBUS, another form genus
-plants were HETEROSPOROUS -both types of sporangia produced in the same cone with MEGASPORANGIA located at the base (thought to have to do with gravity)
-cones known as LEPIDOCARPON are commonly found in some fossil deposits and it is the megasporophylls of these with their sporangia that we may consider as analagous to true seeds
What 3 lines of evolution emerged from the PROTOLEPIDODENDRALES?
1) the herbaceous, eligulate, homosporous Lycopodiales

2) the herbaceous, ligulate, heterosporous Selaginellales

3) the arborescent, ligulate, heterosporous Lepidodendrales
What are some defining characteristics to the Order Isoetales?
-came about in the Permian pd (colder and more diversified climate)... after Carboniferous
-heterosporous
-ligulate
-produces its sporangia adaxially and somewhat sunken into the leaves
-main interst is attached to the short compact axis of the plant, often called the CORM
-first the corm has a cambium which produces secondary vascular tissues towards the inside of the axis wile if forms SECONDARY CORTEX (parynchomous) to the outside
-this meristem may represent a fusion of the 2 meristems of the lepidodendrids
-upper part of the axis is a stem, but the lower part is weird... neither clearly shoot nor clearly root, but produces a succession of roots in a regular arrangement
-represents greatly reduced arborescent lycopods and that their peculiar basal reion is derived from a compressed and reduced stigmarian system by long regressive evolution
-corm of ISOETES is a modified shoot system but in the modern forms this basal structure has been so reduced that it does not reveal its origin in its own development
-this extant group does appear to represent the arborescent, ligulate, heterosporous line of lycopsid evolution
What is the FORM GENUS KNORIA?
-name given to impressions of old wrinkled bark
What is the FORM GENUS LEPIDOPHLOIOS?
-name given to impression/compression fossils of leaf suchion covered stems
What is the FORM GENUS LEPIDOPHYLLOIDES?
-the name given to fossil leaves of LEPIDODENDRON
What is the FORM GENUS STIGMARIA?
-name given to the Rhizophore or root system
What is the FORM GENUS LEPIDOSTROBUS?
-the male cone which yields LYCOSPORA spores from sporangia borne on LEPIDOSTROBOPHYLLUM cone scales
What is the FORM GENUS LEPIDOCARPON?
-the term used for the megasporangiate
What is the FORM GENUS CYSTOSPORITES?
-the dispersed megaspore