Lignotuber

{{short description|Swelling of the root which protects against fire and other hazards}}

{{Use dmy dates|date=June 2023}}

File:Cussonia paniculata - Lignotuber.JPG partly exposed above ground]]

File:Camphor Trees2, Vergelegen.JPG at the Vergelegen Estate]]

File:Lignotuber face Roosevelt Redwood Grove.jpg

File:Lignotuber active redwood.jpg

A lignotuber is a woody swelling of the root crown possessed by some plants as a protection against destruction of the plant stem, such as by fire.{{cite journal |author1=Paula S. |author2=Naulin P.I. |author3=Arce C. |author4=Galaz C. |author5=Pausas J.G. |year=2016 |title=Lignotubers in Mediterranean basin plants |doi=10.1007/s11258-015-0538-9 |journal=Plant Ecology |volume=217 |issue=6 |pages=661–676 |bibcode=2016PlEco.217..661P |citeseerx=10.1.1.707.1505 |s2cid=17448762}} Other woody plants may develop basal burls as a similar survival strategy, often as a response to coppicing or other environmental stressors. However, lignotubers are specifically part of the normal course of development of the plants that possess them, and often develop early on in growth.{{Cite book |last1=Keeley |first1=Jon E. |url=https://books.google.com/books?id=Qx2adrY9AukC&q=umbellularia |title=Fire in Mediterranean Ecosystems |last2=Bond |first2=William J. |last3=Bradstock |first3=Ross A. |last4=Pausas |first4=Juli G. |last5=Rundel |first5=Philip W. |date=2012 |publisher=Cambridge University Press |isbn=978-0-521-82491-0 |language=en}} The crown contains buds from which new stems may sprout, as well as stores of starch that can support a period of growth in the absence of photosynthesis. The term "lignotuber" was coined in 1924 by Australian botanist Leslie R. Kerr.{{cn|date=May 2021}}

Plants possessing lignotubers include many species in Australia: Eucalyptus marginata (jarrah), Eucalyptus brevifolia (snappy gum) and Eucalyptus ficifolia (scarlet gum) all of which can have lignotubers {{convert|10|ft|m|0|spell=in}} wide and {{convert|3|ft|m|0|spell=in}} deep, as well as most mallees (where it is also known as a mallee root{{cite web |title=Mallee Trees |first=Sophie |last=Thomson |website=Gardening Australia |publisher=Australian Broadcasting Corporation |date=14 October 2006 |url=https://www.abc.net.au/gardening/factsheets/mallee-trees/9427326 |access-date=25 May 2021 |others=Series 17, Episode 35 |archive-date=11 November 2020 |archive-url=https://web.archive.org/web/20201111200202/https://www.abc.net.au/gardening/factsheets/mallee-trees/9427326 |url-status=live }}) and many Banksia species.

Plants possessing lignotubers on the western coast of the USA include California buckeye, coast redwood, California bay laurel (aka Oregon myrtle), and multiple species of manzanita and Ceanothus.

At least 14 species in the Mediterranean region have been identified as having lignotubers (as of 1993). Lignotubers develop from the cotyledonary bud in seedlings of several oak species including cork oak Quercus suber, but do not develop in several other oak species, and are not apparent in mature cork oak trees.{{cite journal |title=Lignotuber Ontogeny in the Cork-Oak (Quercus suber; Fagaceae). I. Late Embryo |author1=M. L. Molinas |author2=D. Verdaguer |journal=American Journal of Botany |volume=80 |issue=2 |year=1993 |pages=172–181 |doi=10.2307/2445037 |jstor=2445037}}

The fire-resistant lignotubers of Erica arborea, known as "briar root", are commonly used to make smoking pipes.

The largest known lignotubers (also called "root collar burls") are those of the Coast Redwood (Sequoia sempervirens) of central and northern California and extreme southwestern Oregon. A lignotuber washed into Big Lagoon, California, by the full gale storm of 1977 was {{cvt|41|ft|m}} in diameter and about half as tall and estimated to weigh {{cvt|525|ST}}.{{cite journal |last=Del Tredici |first=Peter |date=Fall 1999 |title=Redwood Burls – Immortality Underground |journal=Arnoldia |volume=59 |issue=3 |page=photo and caption p. 19}} The largest dicot lignotubers are those of the Chinese Camphor Tree, or Kusu (Cinnamomum camphora) of Japan, China and the Koreas. Ones at the Vergelegen Estate in Cape Town, South Africa, which were planted in the late 1600s have muffin-shaped lignotubers up to {{convert|6|ft|m|0|spell=in}} high and about {{cvt|30|ft|m|0}} in diameter.{{cite book |last=Esterhuyse |first=Neels |display-authors=etal |title=Remarkable Trees of South Africa |location=Pretoria |publisher=Briza Publications |pages=102–103}}{{cite book |last=Pakenham |first=Thomas |title=Remarkable Trees of the World |location=New York |publisher=W. W. Norton and Co. |pages=122–123}} Perhaps the largest lignotuber in Australia would be that of "Old Bottle Butt", a Red Bloodwood Tree (Corymbia gummifera) near Wauchope, New South Wales, that has a lignotuber about {{cvt|8|ft}} in height and {{cvt|16.3|m}} in circumference at breast height.{{cite web |url=http://www.nationalregisterofbigtrees.com.au/listing_view.php?listing_id=535 |title=National Register Of Big Trees |access-date=27 October 2017 |archive-date=29 October 2017 |archive-url=https://web.archive.org/web/20171029012437/http://www.nationalregisterofbigtrees.com.au/listing_view.php?listing_id=535 |url-status=live }} A lignotuber should not be confused with a xylopodium. Lignotubers are compact, even round. A xylopodium is diffuse and are sometimes called "underground trees".{{cite book | editor= Paulo S. Oliveira | date= 2002 | title= The Cerrados of Brazil | location= New York | publisher= Columbia Univ. Press | pages= 96, 128-129, 132 | ISBN= 0-231-12042-7 }}

Many plants with lignotubers grow in a shrubby habit, but with multiple stems arising from the lignotuber. The term lignotuberous shrub is used to describe this habit.{{cn|date=May 2021}}