For populations to evolve, mutations are necessary. These changes in the genetic code often go unnoticed but, when they do affect the plant’s development, horticulturists select for the ones that make plants more productive or pleasing to people. In Tuesday’s tree mob, the Director of the Arnold Arboretum Ned Friedman spoke to us about a clearly visible mutation in an eastern redbud tree close to the katsura collection (accession #10-68*B).
Friedman first introduced the botanical term “cauliflory,” a reference to plants that flower from old growth. Redbud is one of these plants. See the photo below for flower buds on the trunk of the tree.
Friedman then pointed out that one branch of the redbud tree had white flowers, in contrast to the reddish-purple flowers on the rest of the tree. Because eastern redbud flowers on old growth, he was able to pinpoint the location on the branch where the mutation knocking out the anthocyanin pigment in the flowers must have occurred. He guessed that the mutation occurred between ten and twelve years ago.
Friedman said that the mutation exists in every cell from that point on the branch onward and, as long as the flowers don’t cross-pollinate with reddish-purple flowers, will be seen in any plants grown from the seeds that develop on the branch.
This tree mob was the first in a series of three tree mobs that Friedman will lead on mutations in plants.
With snow on the ground and a chill in the air, Saturday did not feel like spring. But the birds at the Arnold Arboretum were singing their spring songs. We found large concentrations of birds near the Visitor Center and around Faxon Pond.
The red-winged blackbirds, all males as far as we could tell, were singing loudly. Common grackles, another sign of spring, checked us out with those freakishly white eyes of theirs.
On Sunday, I joined an Urban Nature Walk in the Arnold Arboretum led by Jef. Last year at this time, a few magnolias, cherries, and red maples were blooming. This year, winter still held sway with temperatures in the 30s F, a cold wind, and patches of snow hiding in shadow.
Despite the cold, we found a few plants in flower. Skunk cabbages (Symplocarpus foetidus) were popping up near the marsh.
The rosegold pussy willow (Salix gracilistyla), native to East Asia, was also starting to bloom.
Due to a warm early spring this year, the peak bloom for most of the lilacs at the Arnold Arboretum was the weekend of April 21-22. However, over a month later, a few varieties are still in bloom (date of accession in parentheses):
Syringa x prestoniae ‘Donald Wyman’ (1991) – Donald Wyman lilac
Syringa x swegiflexa (1949) – Swegiflexa lilac
Syringa sweginzowii (1977) – Chengtu lilac
Syringa tomentella (1999) – Felty lilac
Syringa villosa (1907) – Late lilac
Syringa [Villosae group] ‘Mary C Bingham’ (1998) – Mary C Bingham lilac