Florida Citrus?

The citrus family, Rutaceae, includes more than 1,500 mostly aromatic plants in 150 genera. The fruits of commerce — grapefruit, oranges, tangerines, and like — are in the genus Citrus, are primarily of Asian origin, and are greatly plagued by citrus greening, an exotic bacterial disease vectored by the Asian citrus psyllid.  Invasive organisms imperil natural areas and commerce, too.

Three genera in this family are native to Florida and are very different from the commercial crops that once dominated the economy of our area.  The largest genera is Zanthoxylum with 5 species.  Zanthoxylum means yellow wood, and its heartwood is prized for cabinetry.

Two species grow in Indian River County — Hercules-club (Zanthoxylum clava-herculis) and wild lime (Zanthoxylum fagara).  Both are hammock plants, thorny, and have odd pinnate compound leaves.  Hercules-club was planted at the Oslo Riverfront Conservation Area (ORCA) near the DOT culvert crossover as part of a restoration project.  Treasure Shores Park has lots of Hercules-club.  Wild lime grows in a hammock at the Florida Medical Entomology Laboratory. Both plants grow at Pelican Island National Wildlife Refuge.

Hercules-club is more common overall, grows to be a large tree (to 50′), and is deciduous.  Its leaves are elliptical with obvious pellucid dots on its undersides that contain volatile oils.  Crush up a leaf to release these compounds and place it your mouth to find out why this tree also is known as the toothache tree or tingle bark.  After your mouth numbs and you enjoy the pleasant citrusy flavor, spit out the leaf.

Both Hercules-club and wild lime are larval host plants for the giant swallowtail butterfly (Papilo cresphontes), as is commercial citrus.

Wild lime grows in our area as a small tree (to 15′) or a large shrub with smallish ovate leaves that emit a lime-like fragrance when crushed.  Note the distinctive winged (fleshy) rachis (stem)  and sessile (stemless) leaflets below.  It is a secondary larval host for the endangered Schaus’ swallowtail butterfly (Heraclides aristodemus) found in tropical hardwood hammocks in a small area of south south Florida.

Also commonly called prickly ash, wild lime sometimes is deciduous (depending on weather), has nasty recurved spines, and grayish bark …

The bark of the trunk and branches of Hercules-club also bears thorns and is the reason for this common name.

With time the thorns fall away from the conical warty protuberances.

Both of these plants are dioecious (male & female flowers on separate plants) with nectar-rich flowers that attract pollinators as evidenced by the plethora of European bees (Apis mellifera) enjoying the flowers of Hercules-club.

Wild lime flowers are held in the leaf axils (angles).

Their fruits bear no resemblance to the tasty treats of commercial citrus and are termed subglobose (almost round) punctate (marked by dots or depressions) follicles.  They initially are green as shown below on Hercules club.

As they ripen, they become tan and then brown, opening to reveal a shiny hard tiny black seed consumed by birds.

Enjoy seeing these Florida citrus-family trees in the wild and consider incorporating them in your landscape to attract pollinators, to feed giant swallowtail caterpillars, and to feed granivorous birds.  And, don’t forget their value as aromatic as conservational curiosities and shade trees.

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