All is leaf

The Feminist Tree – Clusia rosea

In the last two centuries, humans have made great strides and advances in advocating equal rights for women.  It would be impossible to recite the entire list of grievances suffered by an entire half of the human race throughout our brief history as a species, and even now, things are far from perfect.  But while humanity struggles to find an equal footing for all of its genders (including its non-binary genders), there are a few plants that seem to have things pretty well figured out.  Their solution to the problem of gender inequality?  Just get rid of the males.  One of the most unique among these plants is the species Clusia rosea, which goes by several different common names, but will be referred to in this article as the ‘feminist tree.’

Our story first takes us to the famous Kew Royal Botanic Gardens in Great Britain.  Renowned as being the largest collection of living plants in the world, Kew is also the place where a strange phenomenon was first discovered in plants.  The year was 1829, and an unknown species of plant had just been sent to Kew from Australia by the prominent botanist and explorer Allan Cunningham.  Three individuals of this species had made their way on the long voyage to England, and after careful analysis by a resident botanist, John Smith, it was determined that they were all female, meaning their flowers produced only female sex organs (carpels).  Normally, if there are no males around to produce pollen for fertilization, the female portion of the flower won’t make fruit at all.  You can imagine Smith’s surprise, then, when not only did all three of these strange plants produce fruit, but when he planted the seeds, they grew into healthy new plants of their own (Smith, 1841).  So, barring immaculate conception, how is it possible that plants that hadn’t been pollinated gave rise to viable seeds?  Smith had no real explanation, and the process wasn’t formally described until 1908 when the German botanist Hans Winkler gave it the name ‘apomixis’ (1908).

There are several different types of apomixis in flowering plants, all with very fine-scale differences between them, but they all share a few main component parts.  First, meiosis is either aborted or never takes place.   Meiosis is the doubling and splitting of chromosome pairs that gives rise to haploid cells, the process by which our bodies produce sperm and eggs.  In plants, the production of sperm and eggs is somewhat different from animals due to what’s known as the alternation of generations.  Suffice it to say, however, that with apomixis, meiosis doesn’t occur, resulting in a diploid instead of a haploid egg/embryo (Bicknell & Koltunow, 2004).  This process results in a completely viable seed, which, when planted, will grow into an exact clone of the mother.  From a genetic standpoint, this is not an ideal situation: you want to have as much genetic variation as possible to avoid passing down deleterious mutations, variation that you don’t get when producing clones.  But there are currently over 400 known flowering plants that can undergo apomixis (Carman, 1997), and that number becomes much higher when you take into account other plants that can do this as well (such as ferns), so obviously it has its merits.

This brings us back to Clusia rosea, the feminist tree.  The main benefit of apomixis is that plants can still leave offspring, even when there are no males in close enough vicinity for pollination to occur.  But the feminist tree has taken this to the extreme, because no one has ever found a male of this species; they appear to have gone entirely extinct (Maguire, 1976).  But this species is a rebel in more ways than one.  It belongs to a group of plants called the ‘Stranglers.’  These trees have two types of roots: those that grow in the soil like most plants, and others that grow around nearby trees and vegetation for support.  These aerial roots, as they’re called, grow so tightly around its host that it cuts into the host’s vasculature tissue, eventually killing it.  Once the host is dead and out of the way, C. rosea has more sunlight for itself to use for photosynthesis (Ting et al., 1985).

            Another one of C. rosea’s common names is the autograph tree.  The leaves of this tree are extremely thick and resilient, so much so that you can carve into the supple tissue, which will retain the markings without damage and persist even after they’ve fallen from the tree.  And yet another of its names is the Pitch-Apple tree, so called because it produces a viscous resin in the stems and trunks, which was once used as a caulk for boats (Gilman and Watson, 1993).  The flowers secrete a unique type of resin as well, a habit that is found in only one other family of plants (Euphorbiaceae).  The sticky   resin can be easily seen growing in a ring around the central portion of the flower, and there are certain bees that use it to help make their nests with (Gustafsson & Bittrich, 2003).  In 1992, two compound were extracted from C. rosea that were found to inhibit the effect that HIV had on cells grown in culture (Gustafson et al.)  And finally, the fruit, when mature, opens in a star-like pattern to reveal its deadly contents: bright red seeds that are poisonous to humans.  And all this without the aid of males! 

            It’s unclear how an entire gender in this species went extinct, and do date, no one’s tried to find out.  The feminist tree has a wide range throughout Central America (Maguire, 1976), and it’s hard to imagine something that widespread losing that much diversity.  But regardless of the method by which the males became extirpated (if they ever existed), the feminist tree stands as an example of just how much nature can show us about ourselves and the types of thinking that are now, thankfully, becoming antiquated.  So the next time someone tells you they don’t need feminism, give them a botany textbook.

           

Citations

Bicknell, R. A. & Koltunow, A. M. (2004).  Understanding apomixis: Recent advances

            and remaining conundrums.  The Plant Cell, 16: 228-244.

Carman, J. G. (1997).  Asynchronous expression of duplicate genes in angiosperms

may cause apomixis, bispory, tetraspory, and polyembryony.  Biol. J. Linn. Soc. 61: 51-94.

Gustafson, K. R., Blunt, J. W., Munro, M. H. G., Fuller, R. W., McKee, T. C., Cardellina II,

J. H., McMahon, J. B., Cragg, G. M., & Boyd, M. R. (1992).  The guttiferones, HIV-inhibitory benzophenones from symphonia globullifera, garcinia livingstonei, garcinia ovalifolia and clusia rosea.  Tetrahedron 48(46): 10093-10102.

Gustafsson, M. H. G. & Bittrich, V. (2002).  Evolution of morphological diversity and

resin secretion in flowers of Clusia (Clusiaceae): insights from ITS sequence variation.  Nordic Journal of Botany, 22(2): 183-203.

Maguire, B. (1976).  Apomixis in the genus clusia (Clusiaceae).  A preliminary report. 

            Taxon 25: 241-244.

Smith, J. (1841).  Notice of a plant which produces seeds without apparent action of

pollen.  Transactions of the Linnaean Society of London (meeting of June 18, 1839), 18.

Ting., I. P., Lord, E. M., Sternberg, L. Da S. L., & DeNiro, M. J. (1985).  Crassulacean acid             

            metabolism in the strangler clusia rosea Jacq.  Science 229: 969-971.

Winkler, H. (1908).  Über parthenogenesis und apogamie im pflanzenreiche.  Prog.

            Rei. Bot. 2: 293-454.