This document discusses the systematic position and structure of Psilotum, a genus of tropical fern allies. Psilotum consists of two species, P. nudum and P. flaccidum, which grow as epiphytes in tropical and subtropical regions. The plant body has two main parts - an underground rhizome for storage and anchorage, and an erect or pendent green aerial shoot that arises from the rhizome and is the main photosynthetic organ. Anatomically, the stem has a single-layered epidermis and cortex differentiated into storage and support regions, with a central vascular cylinder of xylem surrounded by phloem. The rhizome has a

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.