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Overview of Berberis Leaf Morphology and
Phenology in N. Hays County

by Bob Harms  email-here
B. swaseyi B. trifoliolata
  1. Leaf Structure

    2. Although a simple leaflet count might seem sufficient to distinguish our two Berberis species, the existence of hybrids requires modification of current keys. To the extent that leaf morphology might be used to recognize hybrids, three factors need to be considered: (Key for our species and hybrids.)
    1. Number of leaflets:
      B. trifoliolata leaves are strictly trifoliate; B. swaseyi generally has (5-)7-11(-13) leaflets; hybrids, (3-) 5-7 (-9) leaflets.
      Some apparent hybrids are also strictly trifoliate, and can be identified as possible hybrids only by inspection of minute floral details (especially stamen morphology).

    2. Attachment of the terminal leaflet:
      With B. trifoliolata this leaflet is always sessile and never stalked; with B. swaseyi it is sessile at the top node of the rachis and always without petiolule, although uncommonly the top leaflet pair may be also be attached at that node.

    3. Presence of a reduced basal leaflet pair:
      Only B. swaseyi has this feature; multi-leafleted hybrids lack it.

  2. Distinctive Characteristics of Leaf Structure in Current Literature. (Contrast our Key.)

  3. Leaf Form & Dimensions.

  4. Leaflet Arrangement on the Rachis.

  5. Petiole Length.

  6. Stipules.

  7. Leaflet Surfaces

    8. Ahrendt describes the B. swaseyi leaflet as "below pruinose grey" and Whittemore gives for both species "abaxially dull, papillose." Although B. swaseyi does have a papillose under surface, none of the current botanical descriptions seem appropriate for our populations.

    B. swaseyi B. trifoliolata
    Additional illustrations and discussion of leaflet surface features.

  8. Leaflet Color Changes

    9. Color of New Leaves
    -
    B. swaseyi spring leaves are yellowish light green; those of B. trifoliolata, reddish. Summer and fall growth of both species varies in color from red and purple to light green, soon turning darker green.

    'Maroon Shift' in Late Fall/Winter
    B. swaseyi B. trifoliolata
    Winter Leaves
    Mature B. swaseyi leaflets take on a maroon cast with the onset of cold weather in late fall. With increased chlorophyll in the spring, these same leaves quickly revert to green.

    -

  9. Sun and Shade Adaptation

  10. Emergence of New Leaves

    11. Although mature plants of both species produce a certain amount of new foliage in response to significant periods of rainfall from spring to late fall, their primary seasons for new leaf formation are quite different:

    26 November 2004 26 November 2004
    B. trifoliolata plants produce new leaves with cooler weather in the fall.

    27 March 2004 8 April 2004
    B. swaseyi forms both flower and leaf buds simultaneously in early spring.
    See also Phenology of Vegetative Growth.

  11. Leaf Fall

    12. Disarticulation

    The manner of leaf disarticulation is common to both species. Leaflets and/or rachis segments detach independently at well developed abscission zones.
    Additional illustrations and discussion of leaf disarticulation.

    Timing of Leaf Fall
    B. swaseyi B. trifoliolata
    Individual leaflets and rachis segments detach throughout the year. This is generally preceded by loss of chlorophyll, with a color change to (brownish) yellow, sometimes also bright red in late fall/early winter (in contrast with the more maroon shift normal for overwintering leaves of B. swaseyi).
  12. Heteroblasty
    Both Berberis species exhibit marked differences
    in leaf form as the seedling/sapling develops.

    Arising from the first node between the narrowly
    oblong cotyledons are several pedicellate, simple,
    suborbicular, palmately veined leaves with a notched
    truncate base and with 7-13 marginal spines.

    The first leaves do not distinguish our two species.

    Additional illustrations and discussion of heteroblasty.

  13. Leaf features indicative of hybridization

    14. Typical hybrid leaves