| B. swaseyi new leaf growth stages. | ||
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| April 2, 2004, leaf flush and inflorescence in bud. | July 3, 2004, leaves darkening/maturing. | July 3, 2004, new leaves, bluish long shoot. |
| B. trifoliolata new leaf growth stages. | ||
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| March 17, 2004, reddish new leaves and small fruit. | March new growth following a rainy winter, 2005. | |
B. swaseyi's new spring leaves are without exception light green, quickly darkening in mid April (noted in 2004 between 4/8 and 4/15). A similar pattern was observed with most hybrids. B. trifoliolata's new leaves are generally reddish, but never match the light green color of B. swaseyi. Later, rain-associated leaves produce a wide range of colors for both species, with reddish tint apparently a function of:
A seasonal period of leaf fall for B. swaseyi immediately follows the period of newleaf maturation, toward the end of April (noted in 2004 between 4/24 and 5/6). Leaflets first yellow and then turn brown before loss. Although limited late spring—early summer leaf fall also occurred with B. trifoliolata, it was not a well-defined widespread event. Both species lose leaflets under prolonged drought. But B. swaseyi is much more strongly affected — during the severe drought of fall—winter (2005/2006) a major loss of leaflets occurred. With the first hard frost leaflets turned bright yellow/red (not maroon) and then brown. Hybrids generally exhibited the same degree of drought resistance as B. trifoliolata, with yellowing leaflets before loss.
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| B. trifoliolata | Hybrid | B. swaseyi |
A survey of rain initiated new stems in mid July 2004, showed:
Our populations are basically in accord with the descriptions of Ahrendt 1961 (p. 2; where our species are genus Mahonia, section Horridae):
- B. swaseyi
- 22 of 31 had bluish-purple shoots; one had numerous green shoots; only 1 plant lacked new stems (as well as leaves).
- Hybrids
- 7 of 10 had reddish-purple shoots; others were green.
- B. trifoliolata
- 5 of 30 had numerous reddish-purple shoots; 5 had neither new shoots nor leaves.
In Mahonia ... the character of the stem is so indefinite as to provide but few data of diagnostic value. The stems are generally scaly, and green at first, though sometimes slightly purplish, ripening to a brownish grey. Smoother dark red stems, such as are familiar in Berberis, appear in the few Mahonia species of the unusual section Horridae. ... In Berberis, the young shoots of the current year are generally greenish, often flushed with a slight reddish tinge on the side facing the sun. Sometimes, after a few week's development, and before first year maturity, the stems assume a vivid red colour, which changes fairly quickly to the more enduring colour of the mature stems.
The labeled stem in the above photograph was extracted in the lower image and the colors red and blue were enhanced to full saturation in Adobe Photoshop. Stage 3 shows no significant trace of blue or red. (From a granitic area in Llano Co., c. 40 miles WNW of N. Hays, with blue-tinted glaucous leaflets typical.)
As stems develop over several months they generally darken, first losing their red pigments, thus enhancing the blue pigments, and finally shifting toward brownish-gray and gray. Although the bluish purple of new B. swaseyi stems appears to be a sufficient but not necessary diagnostic, with older and more mature stems – i.e., with loss of red – this feature is no longer distinctive. My notes for mid July 2004 include:
Two B. trifoliolata plants [T0, T17] seemed to have 2nd and even (for T0) 3rd year shoots that still had areas with a faint purplish tint when observed in early morning sunlight.No purplish long shoots as 2nd year growth were observed for B. swaseyi; all were from the early spring shoots that arose simultaneously with flower racemes.
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| B. trifoliolata: | B. swaseyi: | |
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| 5 consecutive stages along a single stem. | New spring stems in mid summer. | 2 consecutive stages of a mature stem. |