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.