Thank you to Eric Hunt (Eric Hunt@Flickr) for today’s image of Dioon spinulosum taken at the Conservatory of Flowers in San Francisco. Dioon spinulosum is member of the Zamiaceae (one of the few families of cycads), commonly referred to as the sago-palms. This species is native to the Mexican states of Veracruz, Oaxaca, and Yucatan.
Like all cycads, Dioon spinulosum is a gymnosperm. Individuals of Dioon spinulosum have been estimated at ages of 500 to 1000 years old, and plants can reach heights of up to 16m (52 feet) tall, making it one of the tallest presently-living species of cycad! Dioon spinulosum is dioecious, producing one cone (either male or female) per plant about once every three years depending on environmental conditions. This particular species is said to produce one of the largest cones (if not the largest) of any gymnosperm. Female cones (like the one pictured above) can grow to over 80 x 30cm (≈32 x 11 in.) and can weigh up to 18 kg (≈40 lb). Male cones are slightly smaller, measuring around 55 x 10cm (≈21 x 4in.). Dioon spinulosum also forms coralloid roots, which play host to a number of symbiotic nitrogen-fixing species of cyanobacteria.
Cycads are often referred to as “living fossils” (a term coined by Charles Darwin), because their fossil records can be traced through to roughly 300 million years ago. It is thought that they once accounted for 20% of the terrestrial plant species during the Mesozoic/Jurassic eras, meaning they were likely forage for the largest herbivores to walk this planet, the dinosaurs!
However, recent research has discovered that the modern cycad species we are familiar with have appeared out of a “near synchronous rediversification globally around 12 million years ago”, which tragically contradicts a favourite theory of mine that dinosaurs were responsible for the present-day diversity in today’s cycads. See the paper by Nagalingum, N.S. et al. 2011. Recent Synchronous Radiation of a Living Fossil. Science. 334(6057):796-799. doi: 10.1126/science.1209926. (full PDF download). If you are interested in the ideas surrounding the coevolution between dinosaurs and cycads before the 2011 paper, see George Mustoe’s 2007 article in The Cycad Newsletter (Vol. 30(1):6-9): The Coevolution of Cycads and Dinosaurs. For some additional thoughts about the 2011 paper on the recent radiation of cycads and support for why the term “living fossil” may still be appropriate, see Jerry A. Coyne’s article: Paper on “living fossils” finds recent radiation, but misses the point. If all of that doesn’t get your blood moving, then I don’t know what will.
On a conservation note, this species is listed as endangered under the IUCN redlist. It is not alone amongst its cycad peers: approximately 65% of cycads are considered threatened or endangered. Unfortunately, their lengthy reproductive cycle and geographical isolation are not beneficial features when faced with climate change, habitat loss and overharvesting for sale as ornamentals. To learn more about all things cycad and to get involved with conservation efforts, visit the site of The Cycad Society or support the Fairchild Tropical Botanical Garden’s Cycad Conservation Initiative.