BIOLOGY 3404F EVOLUTION OF PLANTS Fall 2008

1. BIOLOGY 3404FEVOLUTION OF PLANTSFall 2008 Lecture 14 Tuesday Nov 11, 2008 Chapter 18, Gymnosperms I: Cycadophyta, Ginkgophyta & Gnetophyta

2. What is a gymnosperm? • Plants that produce naked ovules, exposed on the surface of sporophylls; no ovary wall • There are about 720 species of gymnosperms, versus 235,000 species of angiosperms. • Ovule: a megasporangium (produces female megaspore) within 1-2 layers of tissue called the integument(s)

3. [Pteridosperm-ophyta] Late Devonian (370 MYA) Elkinsia ovules and sporophylls (cupules)

5. Ovules versus ovaries • “Female portion” (gynoecium) of a flower may contain one or more carpels (separate or fused), each considered to be a modified leaf; these are found in angiosperms • “Pistils” (one or more carpels) consist of ovary, style and stigma; pollen lands not on ovule as in gymnosperms but on tip of stigma – “indirect pollination”

6. Late Devonian Archaeosperma ovules (a-b); fossil “seed” (360 MYA) [Pteridospermophyta]

7. Gradual enclosure of early ovules in Pteridospermophyta

9. Progymnosperms: Aneurophytales and Archaeopteridales • Progymnosperms appeared in the Devonian (380 MYA). • These resemble trimerophytes but produced bifacial vascular cambium (see Fig. 18-6 and paragraphs below it), which produces secondary phloem and xylem - i.e., true wood. • Examples are Aneurophyton and Archeopteris (= Callixylon, the name for its trunks); the latter formed large trees in southern Ontario! • What's missing? Seeds!

10. Archaeopteris, and a view of its foliage and sporangia

11. [Wood of Archaeopteris is called Callixylon] Callixylon newberryi wood (polished slab), Devonian, New Albany Shale, Liter's & Clark County, Indiana; same, 50X (photos by Rick Schrantz, Kentucky Paleontological Society: http://www.uky.edu/OtherOrgs/KPS/pages/fossilphoto.html)

12. A radial section of Callixylonnewberryi wood Wood of Callixylon huronensis from Kettle Point, Ontario (~370 MYA)

13. Wood of Callixylon, probably C. huronensis, Kettle Point, Ontario

14. Progymnosperms: Aneurophytales Aneurophyton germanicum, from middle Devonian in Rhineland, Germany. Aneurophyton had a protostele, secondary growth, was highly branched and possibly shrubby, and reproduced by spores (homosporous). Photo by Volker Wilde, from http://www.senckenberg.uni-frankfurt.de/fis/palbot.htm

16. Gymnosperms • 5 phyla of “gymnosperms” are Pteridospermophyta, Coniferophyta, Ginkgophyta, Cycadophyta, Gnetophyta [but see recent evidence placing gnetids in Coniferophyta] • Pteridospermophyta (e.g., Elkinsia, Archeosperma) appeared in the Devonian (365 MYA). • Cordaites is regarded as a primitive member of the Coniferophyta; it was present in the Carboniferous (300+ MYA). • Two of the remaining “gymnosperm” phyla, Cycadophyta and Ginkgophyta, appeared in the Permian (290-245 MYA); the Gnetophyta appear to have come in the Cretaceous (130 MYA).

18. Pteridospermophyta (seed ferns) • Pteridospermophyta (e.g., Elkinsia, Archeosperma) also appeared in the Devonian (365 MYA)! The Devonian was a busy time. • Medullosa (Carboniferous) looked like a tree fern, but produced seeds in cupulate ovules.

19. Carboniferous seed fern Medullosa

20. CYCADOPHYTA: Currently, these are a small group of living fossils, primarily tropical/subtropical, (dominant during Mesozoic, or cycad-dinosaur age, +/- 200 MY bp); 0.5-3 (18) m tall; 11 genera, 275 species [140 in text]. • Cycads have fern-like or palm-like foliage: pinnate, often with "circinate vernation" (unfurling). Common name of some is "sago palms" • [Sago flour is prepared from pith of Cycas circinalis in India & Sri Lanka and C. revoluta in Japan; but also from true palms (Metroxylon and some species of Arenga and Caryota), which are monocotyledons of the Anthophyta].

21. Cycads II 2. Stout stem (mostly subterranean) is mostly pith - despite vascular cambium, there is very little secondary phloem or xylem; growth is slow. 3. Leaves are arranged spirally on stem (usually in a dense tuft at the apex). 4. Many inhabit dry areas such as dry deserts of Australia; Zamia lives in sandy spots in southern Florida among palmettos. Primary roots are well developed (up to 12 m); deep roots and fleshy stems store water.

22. Cycads III 5. Secondary, coralloid roots grow on or above soil, like cypress "knees", and contain symbiotic cyanobacteria (Anabaena) that fix atmospheric nitrogen. [Name 2 other symbioses between plants with nitrogen-fixing cyanobacteria]

23. Cycads IV 6. Heterosporous (goes without saying in seed plants); dioecious (2 homes), so one plant produces male strobili and another produces female, or ovulate, cones. The microgametophyte is wind-dispersed pollen; female cones produce several to many ovules, spirally on an axis; these produce a "pollination drop" (a drop of liquid at micropyle); pollen landing on the pollination drop adheres, and then is sucked into the micropyle to a pollen chamber as the drop dries and shrinks; then grows a pollen tube, down which the sperm swim using their many flagella (undulipodia) to reach and fertilize the egg.

24. Cycads V 7. Although there may have been several archegonia per ovule, only one usually develops into a zygote in the mature seed. The fruit is a fleshy cone

25. Zamia integrifolia [= Z. floridana, named Z. pumilla in your text] in Florida; large grey female cones and smaller brown male cones

26. Female Encephalartos ferox from Africa

27. Female Cycas siamensis with seeds on upper surfaces of sporophylls

28. Sperm of cycads swim to egg (left) after being delivered nearby in a pollen tube (right)

29. GINKGOPHYTA: A real living fossil (I've collected Mesozoic fossil Ginkgo leaves in western Canada) with only 1 genus and species left of its once larger lineage. 1. "Maidenhair tree" has been cultivated for centuries in temple gardens of the orient (first China, then imported to Japan) then imported to botanical gardens of Europe; may no longer grow wild anywhere in the world, although there are reports of a few "wild" trees south of the Yangtze River in China. Makes a great city tree (especially males) because it is highly resistant to smog, and has few pathogens.

30. Ginkgos II 2. A tree to 30+m, with good secondary growth from cambium (or "vascular cambium"), producing secondary xylem (= wood) internally and 2° phloem externally; outer layer of cortex differentiates to form a cork cambium or phellogen, producing a periderm, or bark. Leaves and microsporangia/ovules (dioecious) are produced on short shoots (spurs) from long shoots (branches): gives the Ginkgo a characteristic shape (stem + horizontal, unbranched branches). 3. Leaves are fan-shaped, with palmate venation, and may have central notch (Ginkgo biloba); stomata are produced on the underside.

31. Ginkgos III 4. Pollen (microgametophytes) is produced in microstrobili/microsporangia and is wind-dispersed to the ovules of a female tree. Ovules are paired on a short stalk, or peduncle; each produces a pollination droplet, sucks the pollen in to the pollen chamber, where a pollen tube grows; sperm are flagellated and swim to fertilize egg.

32. Ginkgos IV 5. Although there are 2 (-4) archegonia per ovule, only one zygote develops in the mature seed, and only one of the two ovules develops into a mature "fruit" like a cherry but pale greenish yellow - the integument swells and is fleshy; the flesh causes nausea, but is unlikely to be eaten because is stinks, from butanoic and hexanoic acids; the kernel may be roasted and eaten.

34. Development of male gametophyte and gametes in ginkgo http://www.xs4all.nl/~kwanten/history.htm

35. Ginkgo Petrified Forest State Park, Vantage, Washington Millions of logs were swept by a volcanic mud-flow into “Lake Vantage”, covered in sediments, and petrified (agatized and opalized); 50+ genera of trees are represented in this 16 MYA forest. Some are still found in Western North America (WNA); others in ENA or Asia.

36. GNETOPHYTA: 70 species in 3 genera that are very poorly known - primarily desert-dwellers. The genera are different enough from each other that each is classified in its own order, and may be even less related than that. Originate in the Cretaceous (~130 MYA). [or before!] 1. Xylem of Gnetophytes contains vessel members (together form vessels).

37. Gnetophytes II 2. Ephedra are shrubby or trailing pants with green, jointed stems and minute, ephemeral scale-like leaves; looks like Equisetum (but produces seeds not spores, and has completely different stem cross-section, with secondary growth). 3. Occur in SW North America, South America, southern Eurasia and north Africa. 35-40 species. 4. May be monoecious or dioecious; microstrobili/microsporangia produce wind-borne pollen and megastrobili have 4-7 pairs of bracts, with the upper 1-2 with an ovule in the axil - usually only one develops.

38. Gnetophytes III 5. The ovule may contain 2-3 archegonia, and the micropyle actually extends as a neck, and exudes a pollination droplet, sucks in several pollen grains to the pollen chamber. Pollen germinates to form a pollen tube that grows down the neck of the archegonium, and one sperm nucleus emerges to fertilize the egg - it is non-motile as in conifers and angiosperms. 6. Seed is hard and black, surrounded by red fleshy bracts of megastrobilus.

39. Gnetophytes IV 7. Ephedra is the source of ephedrine, a drug like epinephrine (adrenaline) used to treat asthma, emphysema and hay fever; and used traditionally (e.g., by SW Indians) to treat venereal diseases (E. antisyphilitica). 8. Gnetum is a genus of about 30 species of vine to tree-like plants growing in Brazil, tropical west Africa, wet parts of India, and south-east Asia. Gnetum has large, leathery leaves like a dicot, and fleshy fruits. 9. Welwitschia mirabilis is the only representative of its group, and grows in the ultra-deserts of SW Africa. See Raven et al. and lab notes.

40. Gnetum leaves and megasporangia

41. Gnetum, leaves and microsporangia

42. Gnetum seeds - these are fleshy, but are not true fruits

43. Ephedra, male plants and “microsporangiate strobili”

44. Ephedra, female plant with seeds

45. Welwitschia mirabilis, in Namibian desert, large plant with seeds

46. Welwitschia, male (microsporangiate) strobili (left) and female (megasporangiate/ovulate) strobili, with hemipteran (right)