slender tree called Gnetum gnemon grows in the Garden’s Richard H. Simons Rainforest. It was brought here by now-retired research scientist Dr. Jack Fisher, who gathered it from a market in Singapore in 1985. Passing it, you would not suspect that it has bewildered scientists for generations and remains a taxonomic puzzle. Here is its story. Gnetum gnemon has flat green leaves that are elliptic and occur in pairs, with leaf veins like those of normal trees—a central vein with smaller veins flowing from it. The trunk is upright with whorls of branches from bottom to top. 48 THE TROPICAL Garden The plant bears curious spikes of what appear to be green “nuts” of different sizes, also arranged in whorls to form structures called strobili, or cones. These “nutlike” structures are the developing seeds, which are enclosed in fleshy coverings that turn red at maturity and therefore resemble fruit. Several Gnetum species are lianas: long-stemmed, woody vines that are rooted in the ground and use trees or structures to climb to the canopy. Ten Gnetum species of lianas occur in South American rainforests, two to four occur in tropical Africa and 25 occur in tropical Asia. Only two species are trees. The “g” is silent, by the way. “Gnetum has a long, contentious history,” says Dr. Brett Jestrow, curator of the Fairchild Herbarium. Carl Linnaeus, who gave taxonomy its binomial organization in the 18th century, listed Gnetum with angiosperms, and placed them next to crotons. But in 1907, a description of the family Gnetophyta was published, listing the plant as a gymnosperm and a sister to either conifers or pines. Gymnosperms include conifers, cycads, ginkgos, cypresses, pines and cedars. They bear so-called naked seeds. However, it is more accurate to say that their ovules, the un-fertilized seeds, are naked, since the mature seeds may be covered with a fleshy structure as in Gnetum, Ginkgo, cycads and some conifers. Angiosperms, on the other hand, are vascular flowering plants, with ovary and stigma enclosed in carpels contained in flowers. They appeared after gymnosperms. Flowering plants also are characterized by “double fertilization,” in which two sperm develop in the pollen tube, with one fertilizing the egg and the other creating the endosperm—food for the embryo. Angiosperms have xylem and phloem; they have net or parallel veins. Gnetum does undergo double fertilization, but the second fertilized egg dies and no endosperm develops. Gnetum and two other genera, Welwitschia and Ephedra, are contained in the order Gnetales. You may have heard about Welwitschia, the famously weird wonder of Africa’s Namib Desert that lives for hundreds of years and bears only two leaves. There is only one species, Welwitschia mirabilis. The Garden’s director, Dr. Carl Lewis, once traveled to Namibia just to see this plant. A couple of young specimens are growing in the Garden nursery. Ephedra species, meanwhile, are mostly shrubs and grow in deserts and seasonally dry habitats in both the Old World and the New World. You can find Ephedra in Death Valley in the Western U.S., in the Andes of Ecuador, in the Himalayas and around the Mediterranean. A 2016 paper in the Journal of Systematic Evolution says of the order: “In terms of their morphology and even basic ecology, the Gnetales remain enigmatic, with surprising discoveries continuing to be made.” Or as Jestrow says, the Gnetales are just plain “bizarre.” A Several Gnetum species are lianas: long-stemmed, woody vines that are rooted in the ground and use trees or structures to climb to the canopy.
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