Redwood tree

The swollen tissue at the base of some redwood trees is commonly known as a burl although scientifically it is referred to as a lignotuber . Burls in coast Redwood are masses of stem tissue where elongation of the many stem tips has not occurred. Burls develop from axillary buds in the seedling redwood. This basal burl sometimes called a bud collar persists, growing larger throughout the life of the tree. The dormant stem tips continue slow growth and branching, but do not elongate.
Unlike aerial stems of redwood, burl tissue grows downward. It forms an enlarged mass near the base of the tree above or below the soil surface. Burl tissue overgrows the root tissues at the base of the redwood tree. Redwood burls may also occur well up the main stem and on branches. Their growth is held in check by the presence of chemical signals in a living Redwood. If the tree should die, or even be stressed, such as by low rainfall or fire, the chemical signal weakens or vanishes and the burl will burst forth into verdant life. Burls kept in a shallow pan of water will grow almost indefinitely.
They can also continue on to become a full grown Redwood tree. At the very least, if watered they will produce a lovely fringe of green pseudo branchs and make a very interesting looking and unusual house plant. Redwood burl is a rare commodity. Only about one in one thousand Redwood trees will have a root crown burl, or even rarer yet an above ground burl. Redwood burl is used to produce beautiful artwork, handcrafted goods, and stunning furniture.
Redwoods are incredibly hardy. A live Redwood that gets knocked over will attempt to continue growing via its limbs. If undisturbed, the limbs pointing up will turn into trees in their own right, and this is indeed the source of many row groups of trees. Cathedral or family groups of trees are simply trees that have grown up from the living remains of the stump of a fallen Redwood, and since they grew out of the perimeter, they are organized in a circle. If you looked at the genetic information in a cell of each of these trees, you would find that they were identical to each other and to the stump they sprang from.