Comparison of Internal Structure of Root of Selaginella and Lycopodium

 

Comparison of Internal Structure of Root of Selaginella and Lycopodium

 

Feature	Selaginella root	Lycopodium root
Root origin	Roots commonly arise from rhizophores; they are adventitious in nature.	Roots arise adventitiously from the stem or rhizome.
Root system	Usually delicate, dichotomously branched roots.	Adventitious roots, often dichotomously branched and comparatively firm.
Epidermis / piliferous layer	Outermost single-layered piliferous layer; root hairs may be present in young roots.	Single-layered epidermis or piliferous layer; root hairs may be present in young roots.
Cuticle	Cuticle is absent or very thin because it is a root.	Cuticle is absent or very thin.
Cortex	Cortex is well developed and usually parenchymatous, though some cells may become thick-walled.	Cortex is broad and commonly differentiated into outer, middle, and inner regions.
Outer cortex	Usually compact and protective; may show thick-walled cells in older roots.	Often sclerenchymatous or compact, giving mechanical support.
Middle cortex	Mostly parenchymatous cells with intercellular spaces.	Generally parenchymatous, forming the major part of the cortex.
Inner cortex	Inner region lies close to the endodermis and may be compact.	Inner cortex may be compact and thick-walled in some species.
Endodermis	Distinct endodermis surrounds the stele.	Distinct endodermis surrounds the vascular cylinder.
Trabeculae	Absent in the root; trabeculae are a special feature of the stem in many Selaginella species.	Absent.
Pericycle	Usually one to few layers of cells present just inside the endodermis.	Pericycle is present, commonly one or more layers.
Stele type	Protostele; usually a compact vascular cylinder without pith.	Protostele; compact central vascular cylinder without pith.
Number of steles	Usually one stele in each root.	Usually one stele in each root.
Xylem position	Xylem lies in the center of the stele.	Xylem is central in position.
Xylem maturation	Exarch; protoxylem lies towards the outside and metaxylem towards the center.	Exarch; protoxylem is peripheral and metaxylem is internal.
Xylem arrangement	Commonly monarch or diarch, depending on species and root size.	Commonly monarch, diarch, or sometimes more arched, depending on species.
Phloem position	Phloem occurs around or between the xylem groups.	Phloem lies between or around the xylem arms/groups.
Cambium	Cambium absent.	Cambium absent.
Secondary growth	Absent.	Absent.
Pith	Absent because the stele is protostelic.	Absent because the stele is protostelic.
Special feature	Root is often associated with a rhizophore, which is characteristic of Selaginella.	Shows a compact protostelic root structure typical of Lycopodium.
Main identifying point	Origin from rhizophore and relatively simple protostelic root anatomy.	Adventitious root from stem/rhizome with broad cortex and compact protostele.

Key difference: The root of Selaginella is commonly associated with rhizophores, while the root of Lycopodium arises directly from the stem or rhizome. Both roots are protostelic, exarch, and lack pith and secondary growth.