Bryophytes (Liverworts, mosses, hornworts)

• liverworts are the oldest living land plants and they belong to the marchantiophyta phylum
• liverworts separated first, then mosses, then hornworts. they diverged before evolution of vascular plants
• there are 2 groups of liverworts: leafy and thallose
• Liverworts: ~5200 species - mainly tropical, also common in wet temperate areas (moist), earliest fossils were 380-450 MYA BP
• leafy liverworts: >4000 species, grow in humid shaded environments, gametophyte has leaves which are 1 cell layer thick, rounded lobes, no costa (rib in middle of leaf), in 3 rows (2 large, 1 small amphigastria)
• amphigastria = small, ventrally undifferentiated leaves in leafy liverworts
• in leafy liverworts, some leaves have lobes to retain water
• leafy liverworts grow on many wet surfaces: rocks, logs, soil, and even leaves in rainforests
• there are 3 types of dorsal leaf arrangements: transverse (alternate) succubous, and incubous
• most cells in liverwort stems contain oil bodies (single membrane bound organelles)
• in leafy liverworts, unbranched unicellular rhizoids attach stem to substrate
• leafy liverworts (gametangia): antheridia (on side branches - androecium) and archegonia (at stem tip surrounded by leaves - perianth)
• leafy liverworts (sporophyte -2n): foot, seta (stalk), capsule (where spores are), capsules split lengthwise when spores are mature, spores (1n) mixed with elaters (2n) in capsules
• elaters: long twisted moist cells that surround haploid spores of liverworts, when they dry out they twist and jerk around and scatter spores that they contain
• Thallose liverworts: flat, body stratified in layers, ribbon or heart shaped, bilaterally symmetric
• simple thallose liverworts: body 1 to several cells thick, unicellular rhizoids, in the simplest species the gametangia and sporangia are embedded within gametophyte
• pellia: a simple thallose liverwort with seta and capsule
• complex thallose liverworts: >500 species, gametophyte flat - divided into layers, 10-30 cells thick
• Complex thallose liverworts (gametophyte): lower cells contain large oil bodies and rhizoids, upper cells contain many chloroplasts and raised pores on surface
• gemma cups: found on marchantia gametophyte, formed on gametophyte body, reproduce asexually
• marchantia (a complex thallose liverwort): gametophyte (unisexual, gametangia on gametophores), antheridophore (antheridia on dorsal surface), archegoniophore (archegonia on ventral surface)
• marchantia (sporophyte): seta elongates when capsule matures, neck expands to form calyptra, capsule splits, elaters push spores out
• Hornworts belong to the Anthocerotophyta phylum. There are ~300 species and 420 MYA BP in fossil record. They have small or no protonema
• Hornwort (Gametophyte): thallus is small, 3-4 cells thick (short lived), no oil bodies, 1 chloroplast/cell contains a pyrenoid
• pyrenoid: a protein containing structure present in the chloroplasts of algae and hornworts; center for starch storage
• Hornwort (Gametophyte): archegonia do not surround egg (no venter), antheridia may form in cavities in thallus, or cavities may also be filled with oil or cyanobacteria
• Hornwort (sporophyte): sporophyte is a 1-12 cm long sporangium (capsule), no seta, and basal meristem continuously produces new tissue, has cuticle, stomata, chlorophyll, central columella, multicellular pseudo elaters
• in hornworts, the capsule tip matures then splits and spores are dispersed over months
• pseudo elaters: multicellular structures that are not true elaters but function the same way
• There are only around 6 species of hornworts in BC
• mosses belong to the Bryophyta phylum and there are >10,500 species divided into 3 classes (bryidae, sphagnidae, and andreaeidae)
• Bryophyta are important ecologically because they are found in almost all terrestrial environments, contribute to soil building, improve soil water status, and absorb mineral nutrients quickly
• Bryophyta are usually the first to come back in disturbed areas
• mosses grow in very wet to very dry habitats, hot to cold habitats, and almost ubiquitous on land. they are common as epiphytes on trees, especially in wet habitats.
• There are mosses in Antarctica despite 3000m elevation. they grow because volcanic activity melts snow
• Class bryidae: ~ 10,000 species, >900 species in Pacific Northwest
• Bryidae (Gametophyte): 2 growth patterns - cushion mosses and feather mosses
• cushion mosses: a type of moss where archegonia and capsules (terminal sporangia) are borne at the tips of stems or branches
• feather mosses: a type of moss where archegonia and capsule (lateral sporangia) are borne on short, lateral branches and not at tips of stem