Take Your Dodder to Work

Cuscuta species

Convolvulaceae (or Cuscutaceae)

John is on the road so George used the weekly botany trip to reconnoiter Sandhill Crane Park past the west edge of Palm Beach Gardens for an upcoming “Horticultural Taxonomy” class field trip.  This small park set among wet marshy-flatwoods alongside the C-18 Canal has a boat launch, and maybe boat activity adds a little botanical kick, including more different grasses and sedges than you find in other postage stamp parks.  One of the interesting life forms present is Dodder (Cuscuta), a dandy example of convergent evolution.

Dodder or Love Vine? (Love Vine, by JB)

Convergent evolution occurs when two unrelated plants or animals evolve similarities independently.  For example, porpoises resemble sharks despite absence of relationship, or in our green world, many Euphorbs (Spurges) resemble Cacti to the point of being called “Cacti,” having adapted similarly to harsh desert existence.  Now to the point, South Floridians are accustomed to seeing masses of an orange-yellow-greenish parasitic spaghetti vine festooned over other plants.  This is the native Love Vine (Cassytha filiformis) CLICK  ….(or is it?).  Dodder (species of Cuscuta) can look nearly indistinguishable at a casual glance.  I’m sure I’ve seen Dodder and thought “Love Vine.”

To make up a figure, precisely 99.8703% of the living spaghetti around here is Love Vine, but biomass is not everything.  Dodder is the majority parasite in terms of biodiversity, with at least three species here in Palm Beach County.  These doppelgangers confuse many observers, and would be more confusing if Dodders were more common here. (There are plenty in other regions. Over a hundred species.)    Don’t take this too much to heart, but to my imperfect eye, Love Vines seem to prefer on average larger woodier prey, and Dodder on average tilts toward lower more herbaceous victims, but both have broad tastes, and overlap undermines that feeble distinction.

The two are unrelated.  Love Vine is in the Cinnamon Family (Lauraceae).  Lauraceae  often have a spicy aroma when crushed, and Love Vine crushes a wee bit fragrant, at least to the gullible or to those with super noses.  Flowers of the Lauraceae are unusual for dicots by having flower parts in multiples of 3 (CLICK),  which helps distinguish Love Vine from Dodder with its 5 petals.

Dodder flower with 5 petals and no flaps on the anthers. (GR)

In the Lauraceae, including Love Vine, the anthers open via little flaps instead of splitting open like garden-variety anthers; the flaps are true of Love Vine, but you need a magnifier to see them.  Try it—you can succeed.  Dodder traditionally resides in the Morning Glory Family (Convolvulaceae).  Like most Morning Glories, its fruits are dry, although otherwise variable depending on the species. (Love Vine has a fleshy fruit.)

Thinking back in evolutionary time, it seems obvious, maybe inevitable, that the Morning Glory Family would spawn parasitic members.  Anyone who has ever weeded gardens knows the intimate twining relationships between various weedy “Morning Glories” and the plants they love.  It is only a small step for the twining vine to discover the easy life by penetrating the host to extract the host’s fluids.  Dodders have not gone completely down that road; some (all?) still retain a slight ability to make their own chlorophyll.

Botany has an “oh my” side:  the Secret Lives of Plants:  bloodthirsty carnivores, terrorist poisons, bombastic  fruits, murdered pollinators, and secret symbioses.  An oh my in the air these days is the ability of plants to “smell.”  Outside the blogosphere and into actual plant physiology, plants can truly use chemical signals in the air.  The more we learn about the fine fine fine aspects of gene control, probably the more of that we’ll sniff out.  For example aspirin was originally derived from the plant hormone salicylic acid, a plant-to-plant airborne hormone.  Dodder has garnered attention as a green bloodhound recently for what seems to be an ability to find and even select a host by sniffing.  Just ask YouTube. CLICK and also CLICK

I wonder what a Dodder does when it smells a Love Vine.

I smell a tomato!

 

Love Vine

Cassytha filiformis

Lauraceae

Bee on Conradina (Photo by JB)

John and George explored the Hobe Sound National Wildlife Refuge on the shore of the Intracoastal yesterday, encountering millions of Black Mangrove embryos in the beach debris, some of them taking root.  This was interesting because the dispersal agents are tough, food-laden bare naked embryos without benefit of enclosure in fruit or seed.    We saw Dicerandra immaculata in full bloom left over apparently from a reintroduction effort, enjoyed a bee working over a False-Rosemary (Conradina grandiflora) systematically flower by flower, and encountered a pixieland of mushrooms on the scrubby sugar sand dunes.  

The most imposing and conspicuous (fully) living thing there was the Love Vine draped over trees and shrubs, so we must give it its due.  Love Vine is a nearly leafless scrub-loving parasite resembling orange-tinted spaghetti noodles overwhelming its scrubby shrubby victims.  The botanical name Cassytha comes from Aramaic for “tangled wisp of hair.”  The old name “Woe Vine” fits pretty well too.

To remove a common point of confusion, Love Vine and Dodder look alike but are unrelated examples of convergent evolution.   Dodders are species of the genus Cuscuta in the Morning Glory Family, Convolvulaceae.  Several species live in Florida, with a handful of species in our immediate area.    Although resembling Love Vine, they are far less common and tend to specialize on herbaceous victims as opposed to Love Vine’s preference for bigger prey.

Love Vine (image found on John’s camera after he dropped it fleeing into the woods)

Love Vine (Cassytha filiformis) is a member of the Cinnamon Family, Lauraceae.  Love Vine differs from Dodder by having fleshy drupes (vs. dry capsular) fruits, and by having a feature characteristic of Lauraceae: anthers that open by flaps instead of by the usual slits.   You can see this with a hand lens.   A suggestible observer might sniff the membership of Love Vine in the Lauraceae by a faint spiciness when crushed.   Love Vine has its flower parts in multiples of three, as opposed to multiples of five in Dodder.

Our species, one of about 20 in Cassytha, is worldwide in warm-climate coastal areas.  Apparently the fleshy fruits disperse in part by floating, aided undoubtedly by birds and by storms.

The adaptations of Love Vine for parasitism are profound.  The vine adheres to its host with “suckers” (haustoria) that look like something on a space-alien octopus. 

Love Vine haustoria on oak leaf (photo by JB).

You might think it just sits there and sucks, but the invasion runs deeper.   Tissue from the sucker enters the host and spreads into the hosts cambium (living region just under the bark) and/or phloem (sugar-conducting tissue immediately outside the cambium).  It is never a great idea for a parasite to kills its host.  Although Love Vinosis is sometimes fatal eventually, the attack has a built-in host-sparing restraint.  The parasitic tissue invades the cell walls of its host and draws nutrients out of the host cells across the cell membranes, but the parasitic tissue never actually breaks the host’s cell membranes, thus leaving the host cells alive to keep on feeding.  The recurring idea of harnessing Love Vine as a biocontrol against unwelcome plants may be hobbled by the comparatively nature of Love Vine’s attack. 

On a subcellular level, the xylem (water-conducting) tissues in the parasitic suckers have structures often called “graniferous tracheary elements.”  In plain English, the plumbing at the intake zone has a pressure valve involving tiny granules whose function seems to be to control the stream of incoming stolen sap.    The distribution and roles of these poorly known structures need research.

Around the globe, Love Vine has accumulated numerous uses, ranging from body decoration, to medications, to hair promoter, to potential modern cancer therapy.   As is so often true, the plant contains toxic alkaloids, yet is on the menu in some cultures.    And of course, Love Vine is the active ingredient in love potions.    Happy Halloween.