Comparison of Internal Structure of Stem of Selaginella and Lycopodium

 

Comparison of Internal Structure of Stem of Selaginella and Lycopodium

Characteristics	Selaginella Stem	Lycopodium Stem
Plant group	Heterosporous lycophyte	Homosporous lycophyte
Stem nature	Usually delicate and branched	Usually firm and dichotomously branched
Epidermis	Single-layered epidermis with cuticle	Single-layered epidermis with cuticle
Stomata on stem	May be present in young stem	Usually few or absent on stem
Cortex	Well-developed cortex; often differentiated into outer sclerenchymatous and inner parenchymatous regions	Broad cortex; commonly differentiated into outer, middle, and inner regions
Outer cortex	Generally sclerenchymatous and provides mechanical support	Often sclerenchymatous or compact parenchymatous
Inner cortex	Usually parenchymatous	May be parenchymatous; sometimes thick-walled
Air spaces	Large air spaces may be present around the stele	Air spaces are generally absent
Endodermis	Present as special elongated cells called trabeculae	May be present, but not in the form of trabeculae
Trabeculae	Present; they suspend the stele in the air cavity	Absent
Pericycle	Present around vascular tissue	Present around vascular tissue
Stele type	Mostly protostele; may be monostelic or polystelic	Mostly protostele; commonly actinostele, plectostele, or mixed protostele
Number of steles	One or more steles may occur	Usually single stele
Xylem arrangement	Xylem is generally central and exarch	Xylem is central, exarch, and may be star-shaped or plate-like
Protoxylem position	Protoxylem is towards the outside	Protoxylem is towards the outside
Metaxylem position	Metaxylem is towards the center	Metaxylem is towards the center
Phloem position	Phloem surrounds or lies between xylem regions	Phloem occurs between xylem arms or plates
Pith	Usually absent	Usually absent
Vascular complexity	Stele may be suspended by trabeculae, giving a specialized appearance	Vascular cylinder is compact and not suspended
Special feature	Presence of trabeculae and air cavity around stele	Variety of protostele types, especially plectostele in many species
Main difference	Stele is often suspended in air spaces by trabeculae	Stele is compact, without trabeculae

Major difference: Selaginella stem is recognized by trabeculae and air spaces around the stele, whereas Lycopodium stem has a compact protostele without trabeculae.