Diversity of Angiosperms

• Vessels (except Amborellales)


  • Represent a major evolutionary innovation within angiosperms
  • Type of xylem
  • Specialized water-conducting structures with openings at both ends (perforation plates - contact area of two adjacent vessel members)
  • Wide, elongated dead cells with punctured cell walls through which water flows
  • Evolutionary significance: Larger diameter and open ends, can transport water more quickly and with less resistance, supports greater plant size and complexity
• Amborellales


  • Only have tracheids
  • Imperforate - lack perforation plates
  • Notable for their numerous transversely elongated pits, especially at the tapering end walls where they connect with other tracheid cells
  • Water moves through the pits between tracheids, which slows down the flow but ensures water retention under stress conditions
• Carpel


  • Female reproductive part of the flower; makes up one or more pistils or gynoecium; includes the stigma, style, and ovary
  • Modified, conduplicate megasporophyll bearing two, adaxial rows of ovules
  • Conduplicate = inwardly folded, longitudinally, and along the central margin
  • Evolutionary significance: Conduplicate carpels can facilitate more efficient pollination and fertilization by guiding pollen tubes directly toward the ovules, At maturity the carpel body completely encloses the ovules and seeds, safeguarding them from environmental stress and herbivores, Conduplicate carpels can develop into fruits that protect the seeds and aid in their dispersal
• Monocots


  • Major and distinct group, comprising roughly 56,000 species, 22% of all angiosperms
  • Include the well-known aroids, arrow leaves, lilies, gingers, orchids, irises, palms, and grasses
• Sieve tube plastids with cuneate, proteinaceous inclusions

  • Found in all investigated monocotyledons, with some variation in form
  • Sieve tubes – specialized plant cells found in the phloem tissue, responsible for transporting organic nutrients, primarily sugars from the leaves (where they are synthesized) to other parts of the plant, such as roots, stems, and reproductive organs
  • Cuneate (wedge-shaped)
  • Evolutionary/adaptive significance: If any, is unknown
• Atactostele stem vasculature


  • Consists of numerous discrete vascular bundles that consist of two or more rings
  • May have evolved in response to selective pressure for adaptation to an aquatic habitat, but this is not clear
  • Stele - organization of xylem and phloem
  • Atactostele – type of eustele, found in monocots, in which the vascular tissue in the stem exists as scattered bundles
  • Possible evolutionary significance: In aquatic habitats, plants may experience variable water currents, which could put pressure on their stems. The scattered arrangement of vascular bundles may provide greater flexibility, allowing the stem to bend and sway with the water currents without compromising its structural integrity.
• Parallel leaf venation


  • Veins are either strictly parallel, curved and approximately parallel, or penni-parallel (has a central midrib with secondary veins that are essentially parallel to one another)
  • Ultimate veinlets connecting the major parallel veins are transverse and do not form a netlike reticulate venation
  • Not a characteristic of all monocots (Araceae, Dioscoreaceae - have a reticulate leaf venation similar to that found in non-monocots)
  • Evidence supports the notion that a reticulate venation evolved in these monocot taxa secondarily, after the common evolution of parallel veins
  • Evolutionary/adaptive significance: If any, is unknown
  • Possible evolutionary/adaptive significance: Provides additional structural support to the leaf, helping it maintain its shape and resist mechanical stress.
• Single cotyledon


  • Feature responsible for the name monocot
  • Cotyledon - first leaf of the plant embryo and will be the first part of a plant to emerge from the seed
  • Evolutionary/adaptive significance: If any, is unknown
  • Possible evolutionary/adaptive significance: Primitive trait; may serve as the primary source of stored energy and nutrients during early growth (derived from the endosperm or maternal tissues); some are photosynthetic
• Reduced ephemeral radicle


  • Smaller or less developed, and temporary root of the embryo
  • Subsequent roots of monocot taxa are adventitious
  • Unlike the primary radicle, which originates from the embryo within the seed, these adventitious roots arise from other parts of the plant, such as the stem or even leaves, rather than from the embryonic root system
  • Possible evolutionary/adaptive significance: Roles in anchoring the plant, providing additional support, and absorbing water and nutrients from the soil; allows monocots to efficiently establish themselves in various environments and contributes to their ecological success in diverse habitats; example: brace roots in corn
• Raphide crystals (from Alistamales)

  • Apomorphy for the Alismatales plus all other monocots except the Acorales
  • Secondarily lost in a number of monocot lineages, including many Poales, Zingiberales, and most of the Alismatales themselves (except for the Araceae)
  • Raphides – needle-like calcium oxalate crystals found in various plant organs and tissues; potentially store calcium, sequester heavy metals, protect against herbivory and possibly programmed cell death
• Leaves palmate-netted (Dioscoreales)


  • Leaves are spiral, opposite, or whorled, petiolate, simple to palmate, undivided to palmately lobed, stipulate or not, with parallel or often net (reticulate) venation, the primary veins arising from the leaf base
• Seed coat phytomelanous, all but orchids (Asparagales)

  • Based on recent phylogenetic studies, it is likely that an apomorphy previously thought to unite the Asparagales, the presence of seeds having a seed coat containing a black substance called phytomelan, may actually be apomorphic for all except the Orchidaceae
  • The phytomelaniferous seeds of the Asparagales were lost in some lineages, particularly those that have evolved fleshy fruits
  • Phytomelan – dark, often black, pigmented substance found in the seed coats (testa) of certain plant species; primarily composed of melanin, a pigment that gives it its characteristic color
  • Possible evolutionary/adaptive significance: Acts as a natural sunscreen, absorbing harmful ultraviolet (UV) radiation that can damage seeds during exposure to sunlight
• Commelinids


  • Include a number of economically important plants, including the palms (Arecaceae), gingers and bananas (Zingiberales), and grasses (Poaceae)
• UV-fluorescent cell wall compounds

  • Characterized by an apparent chemical apomorphy, the presence of a class of organic acids (including coumaric, diferulic, and ferulic acid) that impregnate the cell walls
  • Can be identified microscopically in being UV-fluorescent
  • Coumaric acid – one of the phenolic compounds formed during the defense strategy of the plant against wounding and also in lignin biosynthesis
  • Diferulic acid –
  • Ferulic acid – important structural components in the plant cell wall and serve to enhance its rigidity and strength
  • Possible evolutionary/adaptive significance: Defense against herbivores, pathogens, and competitors. Specific compounds may deter herbivory, attract pollinators, or inhibit the growth of neighboring plants, influencing plant interactions within ecosystems.
• Eudicots


  • Comprising roughly 190,000 described species or 75% of all angiosperms
• Tricolpate/tricolpate-derived pollen grain


  • Palynological apomorphy
  • Pollen – immature (not fully differentiated), endosporic male gametophyte, extremely reduced male gametophytes, consisting of only a few cells
  • Has 3 apertures (may function as site of pollen tube exit, to allow expansion and contraction of the pollen grain with changes in humidity)
  • Evolved from a monosulcate type (having a single distal aperture, which is considered to be ancestral in the angiosperms, as well as for many seed plant clades)
  • Many eudicots have pollen grains with more than three apertures, of a great variety of numbers, shapes, and position (constituting important taxonomic characters)
  • These are all thought to have been derived from a tricolpate type
  • Apertures – differentiated regions function as the site of pollen tube exit, allow for expansion and contraction of the pollen grain with changes in humidity, play important roles in pollen germination and fertilization
  • Evolutionary/adaptive significance: Pollen Germination and Fertilization: The colpi on tricolpate pollen grains serve as sites for pollen tube emergence during fertilization. Pollen germination occurs when the pollen grain lands on a compatible stigma and begins to grow a pollen tube through one of the colpi, allowing for the delivery of male gametes (sperm cells) to the ovule for fertilization.
• Asterids


  • Divided into 17 orders
  • Include well-known and economically important plants, such as dogwoods, hydrangeas, blueberries, phlox, tea, borage, gentians, mints, snapdragons, tomatoes/potatoes, carrots, scheffleras, hollies, bluebells, daisies, and a host of others
• Presence of iridoid chemical compounds

  • Evolutionarily, the presence of iridoid compounds can confer selective advantages by deterring herbivory and reducing damage caused by pests and pathogens
  • Plants that produce iridoids may have a higher likelihood of survival and reproduction in environments where herbivory pressure is high
• Unitegmic, tenuinucellate ovules


  • Unitegmic – ovules with a single integument (protective layers of tissue that surround and enclose the ovule)
  • Tenuinucellate – nucellus (central part of the ovule where the female gametophyte develops, provides nourishment and support) is thin or reduced in size
  • Ovule – organ that forms the seeds of flowering plants
  • These ovule features may confer advantages related to seed development and dispersal
  • Single integument and thin nucellus layer may facilitate nutrient exchange between the maternal plant and developing embryo, contributing to seed viability and germination success
• Cellular endosperm


  • Endosperm – primary nutritive tissue for the embryo in virtually all angiosperms, containing cells rich in carbohydrates, oil, or protein
  • Cellular endosperm may confer advantages related to seed viability, germination success, and seedling vigor
  • Plants with well-developed endosperm tissue may have increased reproductive success and competitive advantages in diverse environments