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I saw these lumps on a tree in a park near my house. What are they called?

enter image description here

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    I suspect that there's a specific term for these, as they are all spots where branches were cut off. "Knot" is probably the closest of the suggestions so far.
    – Hot Licks
    Sep 16, 2020 at 12:51
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    I googled "lumps on the trunk of a tree are called", see what it said
    – Decapitated Soul
    Sep 16, 2020 at 14:29
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    @DecapitatedSoul - Which gets you burl, knot, and gall.
    – Hot Licks
    Sep 16, 2020 at 22:05
  • @DecapitatedSoul Correct
    – Damian Siniakowicz
    Sep 17, 2020 at 14:12
  • @KannE You're right.
    – Damian Siniakowicz
    Sep 19, 2020 at 15:08

6 Answers 6

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They are called burls:

a roundish warty outgrowth from the trunk, roots or branches of certain trees.

(Collins Dictionary)

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    Some are, like the one that looks a little like a pig in the OP's picture, but most of the ;umps in the photo are the remains of branches that have been cut off
    – Chris H
    Sep 17, 2020 at 10:18
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At least the more weird-looking ones are called gnarls.

gnarl: A knot in wood; a large or hard knot, or a protuberance with twisted grain, on a tree.

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[Wiktionary]

The word knot may be used for a more prosaic protuberance:

knot: a [relatively] small hard area on a tree or piece of wood where a branch was joined to the tree

enter image description here

[Cambridge English Dictionary]

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    They're all from where the branches have been pruned, I think. I want to say "stump" but that seems to be mainly when the tree is completely cut down.
    – marcellothearcane
    Sep 16, 2020 at 12:19
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    @marcellothearcane all the ones in the picture are knots (or branch scars). LUmps on the bark that did not originate from a branch are called tumors or burls (or UK burr) or gnarls. I thought they called 'warts' or 'galls' but I couldn't find any online evidence for that.
    – Mitch
    Sep 16, 2020 at 13:15
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    @Mitch A gall is a different piece of damage to an oak tree (they may occur on other trees but they are common on oaks). An oak gall or 'oak apple' is caused by a female wasp laying her eggs in the main vein of a leaf. This website will probably tell you more about oak galls than you ever wanted to know!
    – BoldBen
    Sep 16, 2020 at 19:26
  • @BoldBen hmm.. are you saying a gall is the same as a burl or not? what about tumor? which of these is the same and which not? Oh...just visited the site. A gall is not on the trunk at all. Got it.
    – Mitch
    Sep 16, 2020 at 20:43
  • @Mitch Wasn't there a musical, 'Gnarls n' Burls'?
    – Edwin Ashworth
    Sep 17, 2020 at 13:08
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In United Kingdom English these are burrs. See a description and definition at Woodland Trust:

You may have noticed trees with a strange knobbly growth or two on their trunk. They're easy to spot once you start looking! This abnormal growth is called a burr. In American English it’s known as a 'burl', so you may find it referred to as both. This growth is a mass of shoot and bud tissue that grows manically and forms a distinctive growth on the trunk. At its most basic, it's not unlike a benign tumour in an animal.

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If these are tumors, the more scientific name would be galls, although they are sometimes also colloquially referred to as burls. Crown gall is a plant disease caused by the bacterium Agrobacterium tumefaciens (a.k.a. Rhizobium radiobacter). The tumors are mostly smaller, but if they have been there for a long time, they can grow up to ~30 cm in diameter. It's a fascinating story: Agrobacterium injects a piece of DNA from its plasmid into the plant using a sophisticated transfer mechanism, and through this feat of genetic engineering turns induces a tumor in the plant that serves as an exclusive food factory for the bacterium (the compounds produced by the tumor are encoded in the plamid DNA, and only Agrobacterium has the enzymes to break them down and use them as food, so other bacteria or fungi cannot hijack the food source). There are various bacterial strains that differ in the kinds of tumors they make (some are e.g. only on the roots, others on stems).

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In addition to the other answers, there is also knur. (Seems like sort of halfway between "knot" and "burr".)

a hard excrescence (as on a tree trunk)

[Meriam Webster]

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Your photo shows great examples of elongated “branch collars” left on the tree when branches were properly removed. The branch collars have grown over the wounds of the original pruning cuts leaving a pronounced bump at each location.

Branch collars are expanded areas at the base of tree branches which are part of the trunk rather than the branch. These expanded areas contain compartmentalizations zones in the wood which function to keep decay from penetrating into the tree. If the branch collars are wounded or removed along with the branch to make a flush cut at the trunk then the tree loses its strongest area of protection and weaker compartmentalizing zones will need to control decay inside the tree.

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