Thornless Hawthorn

Crataegus spp.

There are two hawthorns in the Park, quite near each other in the southwest triangle and the west triangle. There are over 200 species in the hawthorn genus, so the Wikipedia entry here describes the genus. If anyone can nail down the exact species, please email me. Five Washington hawthorns were planted in April of 2020 along the 19th Street sidewalk adjoining the Park. This variety does have thorns. Both the hawthorns and the honeylocusts have thornless varieties, and these varieties are called inermis, from the Latin for "unarmed." Appropriate, no?

The two within the Park are a broad, spreading, thornless hawthorn with glossy green foliage turning to red to purple in fall. White flowers in May give rise to dark red fruit which persists through the fall. Height is 15-25 feet and spread 15-20 feet.
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Thornless hawthorn in the southwest triangle, looking east, in July.
Hawthorn factoids:
  • ​​As the common name "hawthorn" suggests, the trees bear fruits called haws and most species have thorns that are 2-3 inches long on trunk and branches.
  • The shrubby thorned trees are used for hedgerows in Europe, as the thorns discourage passage.
  • The tree is a rich source of mythologies in northern Europe.
  • Our two Park specimens are billed as thornless varieties (var. inermis). For comparison, check out the impressive thorns on the 19th Street sidewalk trees.
  • The tree has delicate spring flowers, and the deep green summer leaves turn gold to red in autumn.
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Serrated green leaves and fruits in July.
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Just across the path is the other hawthorn in the west triangle.
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Sometimes all the branches don't get the memo that they are supposed to be thornless. Here are two very sharp 2-inch thorns on the tree in the southwest triangle.
Honeylocusts  are also normally heavily covered with thorns, but the three in the Park are thornless cultivars. 
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Flower buds getting ready to open on April 12
Each bud will produce a flower, and each fertilized flower will produce a haw.
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White flowers on May 7.
Not everyone likes the fragrance of the hawthorn flowers, and the British say that the flowers smell like the Great Plague of London.
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Why would a flower smell like rotting flesh?
If rotting flesh attracts flies, and flies are useful for pollination, the rotting flesh smell will help the hawthorn make more hawthorns. 
These small flies in May are delighting in the scent.
Hawthorn haws December.jpeg
The haws on the hawthorn in the west triangle are plump and red in December, just in time for the holidays. The late fruit is a blessing for the birds who eat them when other food is getting scarce.
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Washington hawthorn on 19th Street planted in April 2020, seen here on May 1, 2020.
The Washington hawthorn has thorns and blooms later compared to the two thornless varieties in the Park. The Washington hawthorn is also more resistant to fireblight, a bacterial infection that can damage many fruit trees, including crabapple and hawthorns.
Notice the graft scar at the base of the trunk, and the very subliminal messages about keeping the dogs off the tree pits.
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If you find a tree that has favored qualities, growing another from its seed may result in variable results. Another option is to graft a sprig from the tree you like onto a more mundane tree's roots (the root stock). This of course kills the more mundane tree, but the grafted tree will be a clone of the tree you like. This photo of a hawthorn on the 19th Street sidewalk clearly shows the graft line near the base of the tree. The older hawthorns within the Park also have graft scars but as trees age the scar becomes less prominent.
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Some of the fruits of the hawthorns in the Park and on 19th Street, seen here in June of 2021, have hair-like growths on them. This is due to a fungus in the genus Gymnosporangium. This fungus is a type of rust, which is a fungus that affects living tissues, often requires two different species as hosts in its lifecycle (in this case a cedar and a hawthorn), and has spores that stain a rust color (Dorito fingers). As long as it is not too extensive, we will keep watching the trees without treatment.
Botany 101 Bonus
 
The hawthorns are complete grafts, which means that everything above the graft line has the same DNA. You could also take a fruit tree, like a plum, and graft branches from trees of other distinct but related species. For example, if you have the skill and the time, you could graft branches from apricots, peaches, cherry, nectarines, and almonds onto the plum tree and each scion, or grafted branch, bears its own particular fruit (see four-minute video here for the Tree of 40 Fruits). The rootstock, what the branches are grafted onto, can be chosen for its adaptation to the soil, dwarf growth, or disease resistance.