basic plant biology
current phylogeny based on genomes and transcriptomes
non-flowering plants
flowering plants

evolution of plants

basic plant biology

most plants develop from a fertilized spore which sends out a rhizoid which will be the root system, and a thin protonema strand which will become the shoot
plant cells have cellulose walls which is more firmly attached at the apical end
- osmotic pressures may cause the cell protoplast to shrink away from the cellulose walls initially at the basal end but remain connected via Hechtian strands
some plants are parasitic and need a host plant as they may not have their own root system of photosynthesis system
- many survive by sucking the sap of the host plant, but once they produce their own seed, they may exhaust their host and die with it
most other plants have a basal root system and an apical shoot system (usually with leaves) which have a polarity
- if you cut a stem into a piece, the original basal part will form roots, and the original apical part will form shoots
- the growth hormone auxin (as in rooting powder), flows from the shoots to the roots, presumably related to electric fields
- plants have an electrical polarity with the earth being negative, hence the roots are more negative than the apex of the plant, but the whole plant is negatively charged because of the grounding with the negatively charged earth, and a tree creates a negatively charged electric field around it while the ionosphere is positively charged
vascular trees have a central old core and newer cells in the outer layers, with the cambria outer layer beneath the bark containing the vascular channels which transports sugar nutrients from the photosynthesis of leaves downwards and water from the roots upwards
- hence if you ring bark such a tree and circumferentially cut into the cambria layer, the tree will die
- in the roots:
  - plants have similar genes to animal inner ear hair cell genes and these form hairs at tips of roots to increase surface area for water absorption from soil
  - radial water uptake from the soil towards the xylem vessels in the vasculature follows two paths, the apoplastic route along cell walls and the cell-to-cell path that is comprised of transcellular (across membranes via protein aquapores which can open or close) and symplastic (through plasmodesmata) transport
- the leaves have stomata which can open and close and through which it breathes carbon dioxide and releases oxygen and water from photosythesis
plants have various sensory perception and memory systems¹⁾
- they can detect and respond to heat, sunlight, chemicals, smell, touch, electric fields, gravity and have proprioception
- plant cells are generally able to respond to a wide spectrum of light from far infrared to visible light and to UV light
  - UV and red light (400-700nm) favor photosynthesis, they generally absorb blue light and reflect green light
  - plants communicate in infrared wavelengths of 700-800nm which allows them to ascertain their proximity to other plants, etc
    - close proximity generally results in plants reducing the number of branches
- tropisms are directional growth movements that allow plants to respond to gravity, light, touch, water, salt, and oxygen
  - auxin plays a central role in several tropisms but often excluding hydrotropism
    - auxin-induced ROS production is necessary for gravitropism
      - plant cells contain mobile grains of starch which help guide the up / down gravity position, hence fallen plants straighten up very quickly in response to gravity even if light is uniformly lit all around them and not just coming from above
      - if one removes gravity and directional light, then plants will use their proprioception to determine shoot growth direction
    - auxin is required for hydrotropism in those plants which have auxin-dependent hydrotropism
  - plants may be able to use their root “inner ear hairs” to detect sound and assess soil quality, possible water sources, etc and indeed sending sound waves of 100-1000Hz will cause roots to turn and grow towards that sound source but if higher than 1000Hz, the roots will grow away from the sound source
  - plants can seemingly respond to the sound of flying pollinators and secrete sweeter nectar (making sweet nectar is expensive - up to 30% of a plant's energy production - so it is more efficient to do this only when there are pollinators around) - the flower shape is possibly an amplifier for sound specifically tune to the frequency of the pollinator's buzz, in addition, the flower itself can vibrate in response to the pollinator
  - parasitic plants often find host plants by their smell using receptors at the tip of their vines to ascertain if it is a healthy sturdy suitable host
  - some plants can smell insect pheromones
  - plants can respond to strong wind gusts with electrical signals, but repeated gusts results in reducing signals, but they maintain memory of the event for over a week so they can preferentially respond to unusually dangerous wind gusts and ignore normal winds
    - trees which can bend in the wind can make twice as much wood to strengthen themselves on one side preferentially compared to restrained trees which don't bend
- roots can detect the state of water in the ground and many can actively search for water (hydrotropism)
  - the apex of the root tip has strong electrical activity with similar signals as in the animal brain and is the part of the plant that uses the most oxygen and
    - chopping off the apex of the root tip will result in that root growing straight instead of hunting around
  - plant roots detect water scarcity via:
    - rapid (within a few hours) using chemical signals called reactive oxygen species (ROS), these signals cause a protein known as IAA3 to cluster together in a way that reduces root branching – a vital step to help the plant conserve resources until water becomes available again and helps the plant pause root growth until it finds moist soil again
    - slowly (over many hours) through a slower hormone-based system involving abscisic acid (ABA) and a small number of genes, including those encoding ABA signal transducers, MIZ2/GNOM, and the hydrotropism-specific MIZ1 which contribute to hydrotropism to aid water foraging which many plants are able to do
  - when roots sense a scarcity of water it sends a signal to the leave to close the stomata to reduce water losses, capture less carbon dioxide and reduce growth
- when a plant detects a gust of wind causing deformity or an insect bite, at least two signals are sent:
  - an electric signal which usually quickly dissipates within 20-30cm, and,
  - a hydraulic signal which can even travel to the roots
plants have various ways of communicating with each other:
- release of airborne chemicals is a common way for plants to warn other plants of dangers such as insects
- most plants release chemicals which we sense as being olfactory but which may have other purposes for the plants
- underground root networks generally interweave with each and given that each apex has a neuronal-like electrical activity, they presumably can communicate with each other
- creating sound waves - eg. flowers vibrating in response to the sound of pollinators buzzing, ultrasonic (20-100kHz) clicking of air bubbles in their vasculature sending status information such as stress
- fungal hyphae filament mycorrhizal systems interweave with root systems forming a symbiosis which also may contribute to plant communication mechanisms - fungi play a linking and relay role between trees in a forest providing 10,000x the network capacity of the plant root networks alone as well as exchanging elements and sugars, transporting these between trees
  - carbon in sugars takes 3 days to move from leaves to the roots of a tree, then another 6 days to move 5m to another tree's roots via the mycorrhizal hyphae²⁾
  - but some fungi such as Armillaria with its Golden Mushrooms, are parasites which destroy trees and a single genetic organism can spread over 2000 acres after growing for over 2400 years ³⁾
  - fungal mycelium can navigate through mazes to find the quickest route and the speed of communication between hyphae suggests this is electrical neuronal-like rather than a chemical process

current phylogeny based on genomes and transcriptomes

rhodophyta
glaucaphyta
viridiplantae
- chlorophyta (chlorophyte green algae)
- Prasinococcales
- streptophyte algae grades
  - bryophytes
    - hornworts
    - liverworts
    - mosses
  - lycophytes
  - ferns
  - spermatophytes
    - gymnosperms (non-flowering seed-producing plants)
      - gymnosperms appear to have evolved 319mya as result of a whole genome duplication event
      - conifers
        
        Araucariacieae
        
        Wollemia
        
        Agathis
        
        Collumbea
        
        Araucaria
        
        Pinaceae
        
        Podocarpaceae
        
        Cupressaceae
        
        Taxaceae
      - Boweniaceae
        
        Bowenia
      - Cephalotaxaceae
        
        Cephalotaxus
      - Cycadaceae
      - Ephedraceae
      - Ginkgoaceae
      - Gnetaceae
      - Taxodiaceae
      - Welwitschiaceae
      - Zamiaceae
      - angiosperms (flowering plants) c245mya
        
        basal angiosperms
        
        Amborella, a single species of shrub from New Caledonia;
        
        Nymphaeales, about 80 species, water lilies and Hydatellaceae;
        
        Austrobaileyales, about 100 species of woody plants from various parts of the world
        
        Core angiosperms (Mesangiospermae)
        
        Chloranthales, 77 known species of aromatic plants with toothed leaves;
        
        Magnoliids, about 9,000 species eg. magnolia, bay laurel, tulip trees, black pepper
        
        Monocots, about 70,000 species monocotyledons eg. grasses, orchids, palms, bamboo, irises
        
        these have leaves which grow such that the youngest cells are at the base of the generally long thin leaves - hence you can mow them and they will re-grow like hair does
        
        Acorales (c131mya)
        
        Alismatales
        
        lilioids
        
        Petrosaviales (c122mya)
        
        Dioscoreales (c115mya)
        
        Pandanales (c91mya)
        
        Liliales (c121mya)
        
        Asparagales (c120mya)
        
        Orchidaceae (orchids)
        
        Apostasioideae (2 genera, 15sp SW Asia)
        
        Vanilloideae (15 genera and 180 species, humid tropical and subtropical regions, eastern North America)
        
        Cypripedioideae (Lady Slipper orchids, 5 genera and 130 species)
        
        Epidendroideae (more than 500 genera and more or less 20,000 species)
        
        Orchidoideae (208 genera and 3,630 species)
        
        Boryaceae 12sp drought-tolerant plants Australia
        
        Hypoxidaceae
        
        Blandfordiaceae (Aust)
        
        Lanariaceae (Sth Africa)
        
        Asteliaceae
        
        Hypoxidaceae
        
        Ixioliriaceae
        
        Tecophilaeaceae
        
        Doryanthaceae
        
        Iridaceae (irises)
        
        Xeronemataceae
        
        Asphodelaceae
        
        'core' Asparagales
        
        Amaryllidaceae s.l
        
        Asparagaceae s.l. (includes asparagus, agapanthus, allium, agaves and yuccas)
        
        commelinids (c118mya)
        
        Arecales
        
        Poales
        
        Zingiberales
        
        Commelinales
        
        Ceratophyllum, about 6 species of aquatic plants
        
        Eudicots, about 175,000 species dicotyledons eg. sunflowers, petunia, buttercup, apples, and oaks
        
        these have stems and leaves that grow with the youngest cells at the tips and cutting off a tip will stop the growth there but stimulate new side growths which means pruning them makes them more bushy
        
        evolved early Cretaceous and includes most leafy trees of midlatitudes
        
        basal eudicots
        
        Ranunculales
        
        Proteales
        
        Trochodendrales
        
        Buxales
        
        core eudicots
        
        superrosids
        
        Saxifragales
        
        rosids
        
        fabids
        
        Fabales (legumes, acacia)
        
        Rosales (roses)
        
        Fagales (beeches)
        
        Cucurbitales
        
        Oxalidales
        
        Malpighiales
        
        Celastrales
        
        Zygophyllales
        
        malvids
        
        Geraniales
        
        Myrtales (myrtles, eucalyptus)
        
        Crossosomatales
        
        Picramniales
        
        Malvales
        
        Brassicales
        
        Huerteales
        
        Sapindales
        
        superasterids
        
        Santalales
        
        Berberidopsidales
        
        Caryophyllales
        
        asterids
        
        Cornales
        
        Ericales
        
        euasterids
        
        campanulids
        
        Aquifoliales (holly)
        
        asterales
        
        Asteraceae (daisies)
        
        Escalloniales
        
        Bruniales
        
        Apiales
        
        Dipsacales
        
        Paracryphiales
        
        lamiids
        
        Solanales
        
        Lamiales
        
        Vahliales
        
        Gentianales
        
        Boraginales
        
        Garryales
        
        Metteniusales
        
        Icacinales

non-flowering plants

flowering plants

the first flowering plants evolved around 140mya
50-80% of the main family stems of angiosperms evolved in the warmest period of the Cretaceous from 100-90mya
the diversification leading to the extant diversity of most of the non-monotypic families (56–91%) did not start until the Cenozoic (56-37mya), this occurred in the context of profound changes in terrestrial ecosystems, including a well-documented trend of global warming in the Palaeocene and Eocene⁴⁾

¹⁾ , ²⁾

https://www.youtube.com/watch?v=E8SJlyrEDX0

³⁾

https://www.youtube.com/watch?v=KH9JVy-u5DQ&t=22s

⁴⁾

https://www.nature.com/articles/s41559-020-1241-3.epdf

Table of Contents

evolution of plants

basic plant biology

current phylogeny based on genomes and transcriptomes

non-flowering plants

flowering plants