There it is – on the verbena bush!

We were in Central Park and there were lots of bushes around – and I had never heard of a verbena bush and I certainly would not have been able to recognize one. (I think I did find the bird, though.) At any rate, whenever I think about the Verbenaceae (or verbena) family these days, that incident always comes to mind, and my memory searches through those sunlit bushes, trying to guess which one is the verbena.

The memory is particularly amusing because, according to wikipedia, most plants in this family are tropical – not your basic NYC habitat. Nevertheless, the family is widespread, as we’ll see later. Here in Panama, the lantana (Lantana camara) that grows wild around our yard belongs to the Verbenaceae, as does Michael’s sandpaper vine, Petrea volubilis, and even the teak tree (Tectona grandis).

As does this plant that I’ve seen growing along roadsides, in an opening in the depth of a pine forest, and in the gardens of many of my neighbors.

It’s commonly called porterweed – Stachytarpheta mutabilis (Jacq.) Vahl.

So what do all these plants, including a tree, have in common, that they should be grouped in the same family?

Verbeneaceae – The Verbena Family

The family has about 100 genera and 2600 species, commonly having quadrangular twigs and/or aromatic herbage [University of Hawaii]. If this makes you think of mint, which has its own family but which may be closely related, then look for these additional features, listed the Delta taxonomic identification site and which are illustrated using the porterweed.

• leaves opposite - here you see the leaves attached to opposite sides of a porterweed stem (also a mint feature).

• young stems tetragonal - actually, on the porterweed, every stem I saw, young or old, had edges like these, and of course, this is a mint feature as well.

• flowers usually in inflorescences (clusters) - in porterweed, the flowers are clustered on a long stalk. (Mint inflorescences are either at the end of a stem or adjacent to leaves. Verbena inflorescences have their own stalk.)

• flowers have bracts (bracteate) – bracts help protect the developing flowers; here they cover the flower buds before the bloom and remain behind after the bloom. (No bracts in mints.)

• petals overlap like tiles (imbricate), corolla usually tubular - it’s a bit hard to see the tile-like overlap of the top part of the petals, but you can easily see the tube they make. (Mint flowers are more irregular than this.)

• pollination by insects (entomophilous) - just search for “porterweed” & “butterfly” at Flickr and you’ll find more than 50 images of butterflies feeding on porterweed nectar. (Mints are pollinated by birds as well as bees – and that’s enough for the mint comparisons.)

• very widespread temperate and tropical but absent from central and northern Eurasia – and in the map below is the widespread-ness, showing that it’s not so odd after all that there would be a verbena bush in Central Park.

The Stachytarpheta Genus

Now that it’s clear that the porterweed fits comfortably in the Verbenaceae family, what is it that separates porterweeds from the other 99 genera mentioned by the University of Hawaii?

It’s those long spikes that you see in the first image of the post. The genus name comes from the Greek stachy, meaning “spike,” and tarpheta, meaning “thick.” [Hammer] All members of the genus have them, and a couple of the other common names for the plant in English reflect this appearance: “snakeweed” and “rat’s tail.”

Two other characteristics that separate Stachytarpheta from other genera in the family are [Gentry]

• evenly serrated (sawlike) edges to the leaves - click to enlarge the image and you’ll even see a little tooth at the end of each sawtooth.

• leaf blade decurrent (extending down the leaf stalk or petiole) – here you can see the blade extending down without even enlarging the image.

Both these leaf characteristics are easy to recognize in the field. There are other, detailed, differences between the flowers of Stachytarpheta and other genera, but the long spikes for the inflorescences and the two leaf characteristics are enough in our area for you to identify the genus with confidence.

The “porter” part of porterweed had me puzzled until I read at several sites that some of the species are used to make a porter-like brew for medicinal purposes, the most authoritative source being one from the University of Florida. The concoction is supposedly used for fever, a wash for skin irritations, relief of constipation, and for worms in children [Hammer].

The species mutabalis

The species of Stachytarpheta that is most common around here is S. mutabalis, the one used to illustrate this post, with a pink flower and leaves about 10-20 cm long (smaller toward the top of the plant). A blue-flowered species that may be S. frantzii has smaller and slightly less hairy leaves is also in the area. Since they both attract butterflies, it is not at all surprising that a local “weed” has become a common garden plant, especially one with such an interesting appearance.

Stachytarpheta mutabilis is a neotropical native, being distributed throughout Central America and into South America, but having been spread to Hawaii and eastern Australia.

Verbena and Stachytarpheta

I may never get back to Central Park to look for that verbena bush, but I did find a drawing at the Delta taxonomic identification site that has both a Verbena species and a Stachytarpheta mutabilis drawing side by side. At least I can see them together on my desktop.

About nectar robbery:

…you say “the stingless bee Trigona fulviventris bites holes in the bases of the stamens of L. camara and robs nectar without performing pollination.” Is that right or should it be corollas?

The quote was from the original scientific paper, and he checked that out first. Then he found the explanation:

Aaaah! (Just checked DELTA) [DELTA is an online interactive key for identifying plants. It includes descriptions of families and lists of genera within each family, among many other helpful aids.]

In Verbenaceae the stamens are placed on the corolla tube so if you’re biting “holes below the base of the stamens” you are biting through the corolla I guess.

So technically it’s right, but a bit confusing.
…

Such “robbery” is observed in bumblebees in the UK on a number of plant species where they don’t “fit” the flower. The protective ring is an interesting concept and one I’ll bear in mind when looking at other plants.

We then had a discussion about flower color – why yellow and red? Does the yellow tell the butterfly to get the nectar “here” and does the red tell the butterfly “don’t bother?”

I think you’re almost certainly correct. Changes in flower colour are common in some of the herbaceous Boraginaceae. [The Borage or Forget-me-not family.]

I’ve done a little searching myself and found two more tantillising JSTOR refs!

This article talks about the evolution of flower colour change in Fuchsia exocorticata. The plant has delayed the development of mature red flower colour to
make them easier to spot for the bird pollinator.

This article is rather nice explanantion as to why the flowers might persist in a different colour rather than just wither straight after pollination. It makes the
infloresence bigger and more obvious.

I was also interested in how quickly the flower changes color. The article that started this discussion on nectar robbery mentioned that newly opened flowers are yellow and begin turning orange within 9 hours. One corollary is that the yellow flowers have mostly lost their nectar within that 9 hours.

I checked my plants this morning. As I mentioned to Andee in my reply to her comment on the original Lantana post, these flowers are looking pretty battered at this point in the rainy season.

This morning I saw what I thought was a purely red flower. I now know that I was looking at the buds in the center of the flower.

I didn’t take a picture, but when I went back just after noon today, I saw the outer rim had yellow flowers.

The image is a little blurry because the wind was blowing and I just couldn’t make it stop for my photograph.

I just now checked again (it’s a little past 5 PM) and those yellow flowers have deepened to an orange. By tomorrow those flowers should be red and there should be new yellow ones near the center. I can hardly wait!

Oh, I should mention. Australia is one of those places where L. camara is an invasive species. So is Tasmania. Nuytsia’s comment:

Uuuuugggh bad weed, bad weed.

[In a follow-up note, Nuytsia said that actually Lantana has been eradicated as a pest weed in Tasmania, which he finds an impressive feat "...as it's such a wretched thing." ]

———–

25 October 2006, 09:00

Here’s that same flowerhead this morning. The 7 once-yellow flowers have become orange, 7 buds have opened to become yellow flowers, and the flowerhead itself is somewhat larger in diameter because of the opened flowers. The wilted flowerhead at about 4 o’clock is a little more wilted, and the same color changes have occurred in the other two scraggly flowers.

As a bonus, I watched a wasp-type insect drink nectar from the yellow flowers on a different flowerhead.

Question now is: Is this a thief or a pollinator? Ah, it never ends, does it?

It is Lantana camara, a plant known to and named by Linneaus himself. He gave it the genus name Lantana, which is an ancient Latin name for a Verbena species (L. camara is in the Verbena family). The species name camara is a South American common name for the plant, so Linneaus must also have known where the plant came from.

An English common name for this plant is red sage, yellow sage. The common sage plant (Salvia officinalis) is a member of a different, but closely related family, the Lamiaceae.

Two questions about this plant: 1) why are there both yellow and red flowers in the flowerhead, and 2) is it a weed or a wildflower?

First, more description:

The flowerheads are dome-shaped, made up of many individual flowers, which are tubular and have 4 petals. The buds are in the center of the flowerhead, the young open flowers are yellow, and the old flowers are red. I’ll come back to these colors later.

The plant is a shrub with hairy square stems that may or may not have thorns. This one does:

The leaves are toothed and opposite, a lighter green color below.

What does this plant smell like? My field guide describes the odor as pungent, but I’ve seen many, many descriptions of the aroma. I first saw the smell described on the web as cat pee. I didn’t think it smelled like that, so I began looking for other descriptions. At one site I found different individuals describing the odor as, respectively, “citrus-sage, spicy, [an objectionable] mixture of mint and camphor with a touch of onion, horrible, chicken droppings, none.”

This is an amazing list – it makes me wonder whether the soil where it grows doesn’t have something to do with the smell. Personally, I found the smell fairly strong but not unpleasant, falling somewhere between the citrus-sage description and spicy. The Brooklyn Botanic Garden recommends including L. camara in a “fragrance garden!”

Now, is it a wildflower or a weed? The eternal question. Here in Central (and northern South) America, where L. camara is native, it can be enjoyed for its own sake. It has been cultivated for more than 300 years so obviously has an esthetic appeal. But L. camara is listed in the Global Invasive Species Database because it can be invasive outside Central and northern South American. In Australia, it is listed as a “Weed of National Significance.”

The Global Invasive Species Database does list many uses for L. camara including as a herbal medicine (research in India shows that leaf extracts have antimicrobial, fungicidal, insecticidal, and nematicidal activity.) The shrubs benefit bird species and the flower is a “…major nectar source for many species of butterflies and moths.”

L. camara has been described as an excellent hummingbird shrub that seems even more attractive to butterflies. Which brings me back to the red and yellow colors. My field guide says that the “…old, deep-orange flowers, which persist for some time, provide landing surfaces for butterflies, deter nectar-robbing Trigona bees from accessing the bases of the newer, inner flowers…” This sentence is tantalizing. Nectar-robbing bees?

Further searching on the web turned up an article called “Nectar Robbing and Pollination of Lantana camara (Verbenaceae)” [see references at the end of this post]. It turns out that 1) several flowers in the inflorescence open each day, usually about dawn, 2) newly opened flowers are yellow and start to change color after about 9 hours and the color continues to deepen as the flowers age, 3) yellow flowers contain pollen and nectar but by the time they are red-orange, they have “negligible pollen and no nectar,” and 4) the stingless bee Trigona fulviventris bites holes in the bases of the stamens of L. camara and robs nectar without performing pollination.

The authors learned that with orange and reddish-orange flowers present, the yellow flowers are not robbed as often as they are in the absence of those flowers. Butterflies are the pollinators of L. camara, and the authors suggest that the flower has evolved to feed both its robber and its pollinators.

I haven’t found any studies yet about hummingbirds and L. camara. Here in Panama, birds (flycatchers, honey-creepers, and tanagers) have been seen eating the berries (this according to my field guide), but no word on hummingbirds and nectar or pollination. Many sites that sell garden plants list L. camara as a plant that attracts hummingbirds, but I notice that the Kemper Center for Home Gardening at the Missouri Botanical Garden has not checked the “attracts hummingbirds” box but has checked the “attracts butterflies” box.

Now, at least, I know to keep a close watch on this attractive wildflower/weed. I’ve seen a moth on it, but no bees, butterflies, or hummingbirds. Time to go take a deeper look.

———————-

References:

Favorite field guide: Zuchowski, Willow. 2005. A Guide to Tropical Plants of Costa Rica. Zona Tropical, Miami, 529 pp.

Article in Biotropica: Barrows, E.M. 1976. Nectar Robbing and Pollination of Lantana camara (Verbenaceae). Biotropica, Vol. 8, No. 2, pp. 132-135. doi:10.2307/2989633.

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The common teak tree, Tectona grandis, is a member of the Verbena family (Verbeneaceae). Its leaves are simple, opposite, broadly elliptical. It’s hard to tell from the following picture whether my tree’s leaves fit this description. I got as close as I could, but there are lots of other leaves in the way!

The bark of T. grandis is brown or gray with shallow, longitudinal furrows. I have more confidence that my bark fits this description than I do that the leaf description matches.

But to me, the pattern that made me feel right away that this tree is a teak is the way the leaves droop on the tree itself. Here’s an image from a monoculture teak forest in Costa Rica that shows the pattern pretty clearly.

- compared with the tops of my tree -

Last month I attended a seminar in Boquete presented by Futuro Forestal. This is a company whose goal is to invest in sustainable tropical hardwood forestry. They are growing teak, but they are growing it in mixed stands with mahogany, spiny cedar, native rosewood, and coco bolo. All these hardwood trees are native to Panama except the teak. They make no claims of reproducing a rain forest, in fact they emphasize that they cannot possibly do so. But they’re hoping that forestry like theirs will help take the pressure off timber harvesting within the rain forest. I went to the seminar wearing my BS detectors, but if there was any there, I surely missed it. I do recommend checking out their web site.

What’s left for me to learn is how that teak tree of mine got to the wooded edge of an abandoned pastureland. My first quick searches for seed dispersal on Google Scholar have come up dry, but surely someone knows! I’ll keep looking.