BIOLOGY 3404F EVOLUTION OF PLANTS Fall 2008

1. BIOLOGY 3404FEVOLUTION OF PLANTS Fall 2008 Lecture 9 Thursday October 16 Chapter 16, The Bryophytes

2. The Move Onto Land – Barely Today and next Thursday we will be discussing the bryophytes – Anthocerophyta (Hornworts), Hepatophyta (= Marchantiophyta; Liverworts), and Bryophyta (Mosses). These plants have some adaptations for life on land, but without true vascular tissues (no phloem or xylem, tracheids or vessels) and with aquatic fertilization, they can not grow too far from free water.

5. What is a Bryophyte? • Bryophytes are non-vascular, spore-bearing members of the Kingdom Plantae • Previously, we listed the 5 characters of plants, including bryophytes, that are not found in Chlorophyta*:

6. What makes a Plant? • Protective layer of cells surrounding the male and female gametangia, • Retention of zygote and developing sporophyte within female gametophyte (i.e., within archegonium), • Multicellular diploid sporophyte (multiple meioses per mating event), • Multicellular sporangia (capsules) with protective layer of sterile cells, • Drying-resistant spores with walls containing sporopollenin (a cyclic alcohol), which is also highly decay resistant. (*5 sporopollenin is found in zygote walls of Charophyceae)

8. Riccia, with sporophyte (right) embedded in gametophyte (left)

9. Hornwort gametophyte with sporophytes; note tetrad of spores

10. What makes a bryophyte? • Like Chlorophyta and Tracheophyta, have chlorophyll a dominant, chlorophyll b and carotenoids as accessory pigments • Like vascular plants and some green algae, have cellulose cell walls • Few bryophytes have a cuticle (vascular plants do). • No lignified tissues in gametophyte or sporophyte (present in many vascular plants, esp. perennials) • Sporic meiosis with heteromorphic alternation of generations • Dominant gametophyte phase

11. Cross section of Marchantia gametophyte; multistratose with pores surrounded by specialized cells, the lowermost of which can close off the opening in a manner similar to guard cells of stomata

17. Protonema of a moss, with bud that forms developing gametophyte

18. Bryophyte characters II • Sporophyte (short-lived to annual), though photosynthetic before spore dispersal, is attached to and at least partly dependent on gametophyte (foot cells penetrate and derive nutrients from gametophyte) • Gametophyte generally perennial (a few are ephemeral – short-lived), with a juvenile filamentous phase (protonema) followed by leafy or thalloid structure that produces the gametangia • Sporophyte unbranched and determinate, with a single terminal sporangium (gametophyte may be branched or unbranched, determinate or indeterminate)

19. Bryophyte characters III • Spores (see #5 in first list) generally air-dispersed • Male gametes (sperm) produced in antheridium, a stalked, club-shaped sac with a sterile jacket layer one cell thick (unistratose) enclosing innumerable cells, each of which produces a sperm (remember, no meiosis involved in gamete formation) • Sperm have two whiplash flagella and must swim to egg in archegonium in a water film (another reason bryophytes live in at least seasonally wet places) • Female gamete (egg) produced singly in archegonium, a flask-shaped structure with a unistratose neck and multistratose basal bulb (venter)

20. Antheridium

22. Archegonium; calyptra develops from venter (bulb) of haploid tissue

23. Marchantia sporophytes develop from zygote within archegonium

24. Bryophyte characters IV • Growth of gametophyte is by a single apical cell. Sporophyte has a meristematic zone at the base of seta (compare meristematic zones in vascs) • Generally small – sporophyte usually less than 3 cm tall (often much less), gametophyte generally less than 10 cm, but may be less than 1 mm, or in some aquatic forms as long as 1 meter • Lack roots – have filaments one-celled thick called rhizoids (single celled in hornworts and liverworts, multicelled in mosses) for anchoring and some water and nutrient absorption

25. Bryophyte characters V • Non-vascular – i.e., lack specialized phloem and xylem, and therefore lack true stems and leaves – what we see as stems and leaves are called caulids and phyllids. However, sporophyte stalks (and some gametophyte stems) have water-conducting cells called hydroids (tubular cells lacking protoplasts at maturity, with thin longitudinal and inclined end walls, highly permeable, thus preferred path for water flow). These lack spiral thickenings found in tracheids and vessels. In some mosses, leptoids surround a strand of hydroids – these are food-conducting (as are phloem tissues in vascs), and have degenerate nuclei, but living protoplasm at maturity (common ancestor to phloem and xylem).

26. Hydroids (center) and leptoids in conducting strand in seta of moss sporophyte

29. Sexual features and ploidy • Antheridia and archegonia in same inflorescence (similar to what we call a perfect flower) = synoicous. If not, = autoicous, which may be: • monoicous (antheridia and archegonia in same plant) or • dioicous (different male and female plants) • Sporophyte (= seta and capsule) is diploid outgrowth of zygote from within archegonium; calyptra (if present) is haploid, developed from the venter

30. WHEN? • First fossils found in Devonian (probable origin in Silurian or even Ordovician) • The oldest unequivocal bryophyte fossil is a liverwort – Pallavicinites (very similar to Pallavicinia, which we saw in lab), from upper Devonian (370 MYA) in New York state – probably have it here in Southern Ontario too. • Great liverwort flora in Jurassic/Triassic of Sweden (200+ MYA).

31. Fossil and extant pallavicinalean liverworts. 1. Pallavicinites devonicus, portion of thallus (from Oostendorp, 1987). 2. Pallavicinia xiphoides thallus (from Karssilov et al., 1984). Arrows indicate position of marginal teeth. vis-pc.plantbio.ohiou.edu/ moss/dunn1.html

32. Fossilized spores preserved in 440-470 million-year-old sediments afford the earliest evidence for plant life on land. Were the plants that produced them Bryophytes? Wellman, C., Osterloff, P.L. and Mohiuddin, U., 2003. Fragments of the earliest land plants. Nature, 425: 282-284.

33. WHEN II • Oldest moss is Carboniferous (Pennsylvanian; 300 MYA) – Muscites, close to modern Polytrichum (which is considered an advanced moss). • The best fossil mosses are “Protosphagnales” from Permian (280 MYA) in Russia, with radially-arranged, unistratose leaves, cell arrangement like modern Sphagnum, but no sex organs preserved (or found).

34. WHERE? • From Arctic to Antarctic and everywhere in between, abundant in moist tropics, and a few occur in deserts. • Like lichens, they wet rapidly but dry out much more rapidly. • Some can survive desiccated for months or years and can survive extreme temperatures when dry, but rapid drying or extreme temperatures when wet can be damaging.

38. WHERE II • Epiliths (= saxicolous), epiphytes (= corticolous if on bark, epiphyllous on leaves), on soil (= terrestrial), or aquatic, but not marine • Like lichens, are largely independent of substrate for nutrients, but may have some substrate specificity because of pH or other chemistry, or microclimate. • Tend to be found in moist environments, bathed in surface water, because of aquatic fertilization

39. Bryophyte ecology and nutrition • Bryophytes, like lichens, may take in nutrients through “leafy” tissues of thallus, in addition to uptake through rhizoids and (in a few) via symbiosis with Glomeromycota • Because of this, they are sensitive to the environments where they live: some prefer acidic sites, others basic or calcium-rich sites; some are pollution intolerant, others tolerant • Saxicolous, corticolous, epiphyllous, …

40. Economic Importance of Bryophytes I. Liverworts and hornworts: not much! (but many contain N-fixing cyanobacteria, important in ecosystem nutrient availability; some are mycorrhizal with Glomeromycota) II. SPHAGNIDAE: "economic" importance • 1. Important in hydrodynamics of large areas of especially northern hemisphere - bogs and “muskeg”. • 2. Sphagnum dressings, in medicine, shoes and diapers • III. Other mosses, various other uses

41. BOG FORMATION • a) open pond, slow-moving stream: margins with floating aquatics, especially Carex spp. with roots anchored in Sphagnum • b) Sphagnum builds above (growth) and below (death and deposition) water-line; enables margin to grow inwards • c) increased Sphagnum growth allows colonization of mat by bog shrubs, and eventually conifers such as black spruce & tamarack

42. Bog Formation II • d) continued encroachment of water surface by floating bog mat may eventually cover surface if disturbance is slight. Waves or stream-flow erode edges • e) amelioration of water table by increased Sphagnum mat away from water-line allows development of forest; hummocks may have white pine or white birch • f) in permafrost areas, forest lowers summer temperature of forest floor, permafrost moves upward, water is trapped, and trees are drowned, so open Sphagnum bog cycles with forest

48. SPHAGNUM ION-EXCHANGE MECHANISM • Metal2+ + 2HA ---> MA+ + A- + 2H+ • Gives off H+, lowering pH and eliminating competing mosses (and many vascular plants) • Metal ions can be displaced by shaking in H+ (e.g., dilute HCl) to assay metal content

49. BOG SIDE-BENEFITS a) Bog fossils b) PEAT (1.5m = 6,000y): for fuel and horticulture c) Conservation aspects: exploitations and emissions d) Carbon sink – unless climate warms!

50. Sphagnum dressings, in medicine, shoes and diapers • Absorbs 16-20 X dry weight in water (cotton 4-6); comfortable; mildly antiseptic (vs diaper rash, gangrene) • Sphagnum dressing used greatly in wars: Russo-Japanese (1904-5); WW I (both sides). Millions of dressings made by thousands of volunteers a) crude sphagnum collected, partially air-dried, cleaned of debris, and sorted. b) wrapped in sewn gauze c) sterilized before use by autoclaving or with antiseptics d) preferred species was S. papillosum; also used were S. palustre, S. imbricatum & S. magellanicum