Systematic position and structure and Psilotum

1. Systematic position and Structure of Psilotum
Sankrita Gaonkar
Assistant Professor in Botany
sankrita002@gmail.com

2. Contents
• Systematic position of Psilotum
• Morphology and anatomy
• References

3. Systematic position
• Class: Psilophyta
• Order: Psilophytales
• Family: Psilotaceae
• Genus: Psilotum

4. • Consists of 2 spp. – P. nudum and P.
flaccidum
Distribution:
• Grows as epiphyte in tropical and
subtropical regions
• Abundant in Florida, Jamaica,
Mexico
• In India – P. nudum – Bengal,
Assam, MP
• Common in – AP, TN, MH, Kerala
• P. nudum – grow erect and dwarf,
epiphytic forms grow pendent
• Plant body – 2 parts –
• a) rhizome
• Inside soil, dichotomously branched
– due to injury or variations in
meristematic tissue, bear scales
• Lack true roots
• Harbours endophytic fungus
• Bears filamentous rhizoids –
anchorage & absorption

5. • Covered with cuticle
• b) an erect or pendent green aerial
portion
• Arise from rhizome
• Light considered to be causative
factor in inducing rhizome tip to
grow into aerial shoot
• If we bury growing shoot in soil –
grow into rhizome than shoot
• Shoot – green, dichotomously
branched – main photosynthetic
organ
• Leaves - scaly

6. Anatomy:
Stem:
• Outermost epidermis – single
layered with cuticle (cutin and wax)
• Stomata present – subsidiary cells
absent
• Cortex – differentiated into 3 well
marked regions
i) outer cortex – thin-walled loosely
arranged chlorenchymatous, elongated
cells – contain starch grains
ii) middle cortex – elongated
chlorophylless cells – thickened cell
walls – few or no starch grains
iii) inner cortex – several layers of cells
– reduced thickness of cell walls as
proceed towards stelar region – starch
grain present – region called as storage
region

7. • Vascular region
• Single layer of pericycle and endodermis
• Consists of xylem surrounded by phloem
• Variations in vasculature of rhizome and shoot:
• i) In rhizome – protostele – central core of xylem surrounded by phloem, pith
absent
• ii) transit zone between rhizome and aerial shoot – actinostelic protostele
• iii) middle of shoot – siphonostele
• iv) apical region of shoot – triangular stele, xylem split into 2 distinct patches
• Xylem is exarch in all cases

8. Rhizome:
• Well defined epidermis
• Broad zone of cortex
• Outer cortex – fungus zone
• Middle cortex – starch storage
• Inner cortex – tannin
• Endodermis surrounding pericycle
• Protostele

9. Leaf:
• Without vasculature
• Made up of chlorenchymatous cells surrounded by epidermal layer (devoid
of stomata and chloroplast)
• Chlorenchyma continuous with shoot chlorenchyma
L.S. of Psilotum leaf

10. References
• Vashishta BR. 2010. Botany for degree students:
Pteridophytes. S. Chand & company ltd.