Cycadales

1. Cycadales Sharanya K P Department of Botany NSS College Pandalam

2. Cycadales include both living (extant) and extinct genera • Originated in the Upper Triassic period of early Mesozoic era abt 200000000 yrs ago • Flourished in Jurassic period

3. 0 Cycads Appeared on Earth 250 MYA • Reached their greatest abundance and diversity during the Jurassic • Declined sharply during the Cretaceous radiation of the angiosperms.

4. Global Distribution of Cycads • Cycads are found across much of the tropical and  subtropical  parts of the world. • They are found in America, Australia, Japan, China, India, Srilanka, Madagascar and Africa.

5. Members show difft habitats : xerophytes/ halophytes, wet rain forest,  sand/rock, O2 poor swampy bog-like soils rich in org. materials,in full sun/ shade/both. • Fossils include organ bearing generas : • Nilssonia– leaves, Bennia – seed, Androstrobus - pollen • Classification • Variously classified • Sporn – 1965 – 2 families – Nilssoniaceae (fossils), Cycadaceae (10 living genera) • Bierhorst – 1971 – 3 extant families • Cycadaceae – Cycas 1ly • Stangeriaceae – Stangeria 1ly and  • Zamiaceae – 8 genera ; Zamia, Dioon, Macrozamia etc

6. Cycadaceae • 10 extant , 1 extinct (Paleocycas) genera • Living genera include Cycas – 20 sp, Zamia ;20-40 sp, Dioon;3-5 sp etc • At present there are only 10 genera with 107-117 sps • Living genera- man’s attention-save fr extinction • Their superficial resemblance- sometimes confused with and mistaken for palms or ferns but -distantly related to either. • Also resemble with Bennettitales, Pentoxylales, Cordaitales etc

7. 0 Mexican Cycads Dioon Ceratozamia

8. 0 Australian Cycads Macrozamia Macrozamia

9. 0 African Cycads Encephalartos Stangeria

10. 0 Encephalartos in Africa Encephalartos in Africa

11. 0 Only Cycad Native to the US Zamia pumila

13. External Features • The basic growth form of a cycad is a central “trunk” with leaves spirally arranged at the top • STEM : thick, slow growing, unbranched/ branched • LEAVES : spirally arranged, foliage leaves, pinnate/ bipinnate, circinate vernation,leaflet – dstinct midrib (Cycas, stangeria), persist for 3-10 yrs – drop; base persist - persist longer helios.bto.ed.ac.uk/bto/microbes/nitrogen.htm http://www.damer.com/pictures/travels/southafrica/transvaal2.jpg

14. Produced in crowns at tip of stem Pinnately compound 0 Cycad Leaves

15. Cycas revoluta In Cycas, Dioon leaves – dimorphic, within a single phyllotactic series there are zones of green pinnate veg leaves + zone of brown cataphylls (simple, hairy, long, sharply pointed scale leaves)

16. New flush of leaves

18. 0 Cycad Stems • Columnar • Little branching • Not very woody

19. 0 Certain roots in Cycads grow toward the soil surface Corraloid Roots

20. Corraloid root Cycas

21. 0 A Closer Look at Coralloid Roots • Grow upward near soil surface • Branch to form masses • Root cortex inhabited by Cyanobacteria(carry out nitrogen fixation)

22. Coralloid roots in Cycads • (a synapomorphy of cycads) • These roots grow up rather than down and can be seen above ground. They have symbiotic blue-green algae Cross-section of coralloid root showing layer of blue-green algae (a nitrogen fixer). (Dioon spinulosum) Image from Wayne’s World

23. ANATOMY STEM C S • Roughly circular in outline • Massive peripheral cortex and central pith • Both traversed by mucilage canals • VB conjoint, collateral, open, endarch • Girdling Leaf traces are present • 2o X amount less – compensate by persistent leaf base- manoxylic wood • Monoxylic 2o growth – single cambial ring ROOT C S • Roots – very thick at base • Polyarch – 8 X and P bundles • 1o X exarch

24. Internal str.of leaf-let • Leaf epi – highly cutinised • Sunken stomata – haplocheilic • If midrib unbranched – transfusion tissue is seen on either side of midrib

27. 0 Cycads – Reproductive Structures

28. Cycads produce pollen and seeds in cones • Cones develop at apex of stem

29. 0 All Cycads are Dioecious(The individual plants are either all male or all female ) • Individual plants produce either pollen cones or seed cones Pollen Cone Seed Cone Cycas revoluta

30. Female cone and Male cone

31. All living genera except Cycas bear compact female cones (megasporophylls arrange compactly around a central axis) – terminate fem pls • Growth continue - another bud near base of fem cone – wh pushes cone to 1 side – sympodial growth • In Cycas fem pls –spirally arranged megasporophylls- alternate with cataphylls and foliage leaves- loose megasporangiate zone (very primitive) – monopodial growth (apical growth continues) • Usually 1 cone at the apex, sometimes 2 may appear • Cone size varies – Dioon (2 feet), Macrozamia (75 cm long), Z. pygmea (2 cm)- smallest • Megasporophyll (Ms) have distal sterile laminate portion + stalk like portion – bear 2-3 ovules- micropyles towards cone axis.

32. The megasporophylls for Cycas is leaf-like with ovules at the base. The enlarged one has been fertilized and is developing into a seed

33. 2 views • Cycas Ms – most primitive – leaf like nature • Course of evolution – laminate distal part reduced + no. and size of ovule • Stobiliferous cycads Ms – 2-3 ovules – distal part laminate but not leaf like+ never peltate ( intermediate stage) • Final stage – advanced – peltate Ms – Zamia, Macrozamia – 2 ovules • Ovules foliar in origin – cycads are phyllospermous • Another view – peltate primitive; -open fem organs of Cycas – peltate sporophylls regarded as sporangiophores instead of sporophylls - so ovules are cauline in origin and cycads are stachyospermous

34. Cycadaceae Zamiaceae Megastrobilus / • Female cone ♀ • megasporophyll • megasporangia

35. Cycas circinalis

38. Ovule – sessile, a nucellus + single integument with distinct micropyle • at maturity – 1/3rd of nucellus 1ly free fr Integument at micropylar region • Integument 3 regions – outer and inner fleshy, middle stony • Nucellus – parenchymatous – sub epidermal cell – MMC RD– 4 megaspores –3 degenerate [micropylar region] - 1 functional – fn megaspore • Fn megaspore enlarge – nuclei divide [1000] – wall formation fr periphery [centipetal]– later cellular mass –wh is the female gmtophyte • As gmtphyte dvlp- nucellus extend apically forming solid nucellar beak – extend into micropyle

39. Later archegonial initials [2-10] appear at the micropylar region of female prothallus • All dvlp to archegonia • Each initial –TD- outer 1o neck cell [prd 2 neck cells by 1 more div] + an inner/ central cell. – enlarges – bfr ferti divides to prd small ventral canal cell + a massive egg cell. • Nucellar cells form a jacket layer • Bfr ferti – nucellar tissue separate pollen chamber nd fem gmtphyte break- disappear – 3 celled spore enter arche. Chamber – VCC degenerate- fertilisation – 2n oospore – polyembryony [sev. Archegonia fertilised – but 1 get maturity]- others degenerate – seed form –integument ; seed coat

41. In Zamia the megasporophyll is highly reduced to a stalked, peltate-like structure. They are organized into a simple cone.

42. Male cones are terminal except Macrozamia (arise in axil of leaves) • Compact, central axis bea numerous spirally arranged microsporophylls • Msp – simple conical strr.- distinct fertile and sterile regions (distal end produce to single spinous projection in Cycas, Dioon, Macrozamia), 2 in Ceratozamia, absent in Zamia • Microsporangia on abaxial/ lower surface – appear as mass but in distinct gps of 1/more. These gps are sori • No. varies; 1000- lesser (50/5/6) • Sporangia dehisce – longitudinal slit • Eusporangiate dvpt

43. Microstrobilus/ Male cone ♂ microsporophyll microsporangia

44. A microsporangium has massive wall made up of several layers of cells • Hypodermal cell – microsporangial initial – 1o wall cell (sporangial wall)+ 1o sporogenous cell (sporogenous tissue – outer single layer – tapetum, rest – MMC – microspores/ pollen grains- arranged in tetrads) • Pollen grain – pioneer of male gametophyte • Each microspore with 2 spore coat – outer exine – thick, inner intine – thin along top and bottom of spore- thicker along sides of microspores, so spore has distinct upper and lower end • Big centrally located nucleus + dense cytoplasm • Microspores germinate within microsporangium [precocious germination] as in heterospory

45. Male cones are also simple with each microsporophyll a modified leaf (forming a stalked peltate structure).

47. Nucleus divide – small prothallial cell+ large sister cell – generative cell + a tube nucleus [free within gametophyte] • At this 3 celled stage semi germinated microspore released from microsporangium • Pollination – wind • Pollen caught to Ms – in pollination drop – dries , pull to pollen chamber • 3 celled microspore germinate on nucellus • Each pollen – pollen tube - penetrate nucellar tissue, along sides of pollen chamber • Generative cell – stalk cell [small, contact with prothallial cell]+ body cell [- 4m 2 spermatozoids – muliflagellate]

48. Cycadaceae Male cone and Cataphylls (a synapomorphy) of Cycas taitungensis (native to Taiwan) www.pacsoa.org.au/cycads/Cycas/taitungcone.jpg

49. 0 Many Cycads are Pollinated by Insects • Only a few cycad species studied • Weevils and oldest known bee genus (Trigona) • Usually pollinators mate and lay eggs within female cone • All cones except Stangeria produce heat. Thought to volatilize pollinator attractants • Hence insect pollination may predate flowering plants Trigona weevils