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Specialized Stems

Although the stem is the most evolutionarily ancient plant organ,
many plant species have highly derived stems with specialized form and function.

    Rhizome

    A rhizome is an underground stem.
    It can be distinguished from a root
    by the presence of nodes,
    from which new aerial stems may emerge.

    Ferns and many other plants propagate
    asexually via rhizomes.

    Tuber

    A tuber is a rhizome modified to store
    nutrients and starch.

    The most familiar example is a potato,
    but wild tubers have been an important
    food source for hunter-gatherer humans
    for thousands of years.

    Tendril

    A tendril is a stem modified for clinging and climbing.

    (Tendrils also can be modified leaves.)

    Tendrils are positively thigmotropic:
    they grow towards areas of physical contact.

    Stolon

    A stolon is an aboveground stem that grows horizontally.

    It takes root at points along its length and sprouts new plants.

    Stolons are another means by which plants can propagate asexually, producing a clone.

    Bulb

    A bulb is an underground stem consisting of
    • a dense basal plate (short stem axis)
    • shoot primordium
      ...enclosed by thick, fleshy leaves.

    In some cases, the leaves function as
    nutrient storage reservoirs during dormancy.

    Old leaves dry and form a protective tunic
    around the fleshy, nutrient storage leaves.

    One particular bulb plant will be so
    familiar to you, it will make you cry.

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    Corm

    Like a bulb, a corm contains
    • a basal plate
    • a thin tunic
    • a central shoot primordium

    It lacks visible storage leaves,
    which distinguishes it from a bulb.

    Plants that develop from corms include
    gladiolus, freesias, crocus, and hyacinth.

    Pseudobulb

    A pseudobulb is a modified stem unique to orchids.

    They are thickened, bulblike stems that store both water and nutrients.

    Cladophyll

    A cladophyll is a flattened stem that serves the photosynthetic function of a leaf.

    The term is derived from the Greek

    • clad, "branch"
    • phyll, "leaf"

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    Thorn

    A thorn is a sharp, protective modified stem.

    Not all plant poky-bits are stems.
    They also can be derived from

    • sclerified, pointed epidermis ("prickle")
    • sclerified, pointed leaf ("spine")
    • sclerified, pointed trichome ("bristle")

    Thorns and spines have vascular tissue traces.
    Prickles do not.

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