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The Berberis Flower

by Bob Harms  email-here
Although flowers of our two species are very similar, differences in both size and shape of various components were found. (Detailed descriptions of stamens and the gynoecium are given on separate pages.) Hybrid flowers are of two types:
  1. those with shorter pistils (2.7 mm. or less)
  2. those with longer pistils.
The flowers of group 1 have virtually identical dimensions as those of B. swaseyi. Group 2, however, is characterized not only by longer pistils - similar to B. trifoliolata, but by increased length of all components, quite unlike B. trifoliolata.


B. swaseyi


B. trifoliolata


B. swaseyi flower components.

B. trifoliolata flower components.

Sepals differ not only in size but also in form. The inner sepals of both share a suborbicular central portion with a strongly narrowed base (ratio c. 70:30), but B. swaseyi additionally has an elongated apex that accounts for most of the total length difference. The base of the B. trifoliolata sepal is also much narrower. The middle sepals are smaller versions of the inner sepals with the exception of a more gradual and reduced narrowing of the base. Outer sepals show much greater variation in shape, from elongated to suborbicular, with length:width ratios of 2.25:1 to 0.9:1.

Tables 1 and 2 present the relative average lengths of the flower parts. Table 1 shows that B. trifoliolata has relatively long pistil and stamen lengths, but its petals and sepals are slightly shorter than those of B. swaseyi. Its petals are significantly narrower, giving a length width ratio of 1:1.9, in contrast with 1:1.55 for B. swaseyi.

For measurement details, click here.

Table 1. Relative flower part lengths.
Pistil Stamen Petal Sepal 1 Sepal 2 Sepal 3
     Key:
      = B. trifoliolata
= B. swaseyi
 = Hybrid with pistil < 2.8 mm
= Hybrid with pistil > 2.7 mm

Table 2 presents the same relations plus averages in millimeters by plant species/type. For all types, from pistil to stamen to petal to the first series of sepals the length increases at roughly 31% at each step, then decreases about the same amount to the middle series of sepals, and decreases sharply, almost 40%, to the outermost sepals.

Table 2. Flower Part Lengths (mm.)

The Petal Apex


B. trifoliolata (entire and emarginate petals).

B. swaseyi (emarginate and entire petals).

(To view B. repens flower with significantly deeper notch at petal apex. )

Ahrendt notes (p. 17) that:

In the genus Mahonia, the emarginate petal is even more predominant, there being recorded only four species with entire petals.
indicating that one of these is B. trifoliolata (p. 352; he had no data for B. swaseyi flowers):
Petals entire, shorter than the suborbicular inner sepals.
Both of our species exhibit emarginate as well as entire petal apices, although B. swaseyi is predominately emarginate, with a narrow cleft c. 0.5 mm deep (roughly 10% of petal length). Emarginate petals with a broader notch are more common with B. trifoliolata on the tract with both species, but entire petals are not rare. Outside our immediate area, in the absence of B. swaseyi, entire margins are the rule. One trifoliate plant with a number of B. swaseyi characteristics, T23, has entire petals.

Hybrid plants also show both types, but with no clear correlation between petal apex type and pistil length - although those plants with shorter pistils, a B. swaseyi feature, have entire petals, normally a B. trifoliolata feature. Two hybrid plants had petals of both types.

Number of hybrid plants with entire or emarginate petal apices.
  pistil > 2.7 mm pistil < 2.8 mm
emarginate 5 0
entire 4 3