Best-kept secrets of your neighbor’s yard part 2: Guava flowers

It’s guava flower season!  If you’re in California or the South, there’s a very good chance that someone who lives next to you is using pineapple guavas (Acca sellowiana) for their hedges or shrubbery.  These Argentinian natives (also called feijoas) don’t always set fruit, but their flowers are a great snack all on their own.

Pineapple guava flowers peeking out from the Berkeley shrubbery.

Look for bright red clusters of stamens on tall shrubs with grey-green leaves.  Then make sure that the cluster of stamens is surrounded by 4 petals: light pink on the outside, and pink-purple on the inside.  On the best ones, the petals will be a little bit spongy.  Pluck off the petals and try them (the stamens are edible too, but don’t taste like much).

On the best guava flowers, the petals have curled so that you mostly see the light pink spongy exteriors.

Delicious, right?  Soft, juicy, sweet, with a kinda spicy tropical tang.  If you’ve ever had guava Kern’s nectar, you recognize the flavor, because it’s the same plant.

Pineapple guavas need 50 hours of cold to set fruit, don’t set well in high temps (90 degrees or higher), and many cultivars also need a pollinator, so if you’re in a very warm climate your new snack may never mature into fruit.  Still, it’s best to be optimistic and leave the stamens and pistil attached to the shrub–if you’re lucky in a few months there will be egg-sized leathery looking green fruits to eat as well.

Pineapple guava fruit. Photo by HortResearch via wikimedia.

I will confess to often liberating guava petals from their owners without asking permission, but it’s probably better to tell your neighbor that you’d like to eat their shrubbery.  Ideally, they’ll not only be happy to let you have at it, but gratified to learn about the tasty treat in their yard.

Special thanks to my college adviser Dr. Daniel Martinez, an Argentinian native himself, who introduced these to me back in the day.  And a tip for fellow folks at the Stanford med school: the bushes next to the patio at LKSC should be full of these any day now.

I’m also told they’re a popular cultivated fruit in New Zealand.  Can anyone confirm?


Steel magnolias: using magnolol to combat arthritis

The gorgeous display of magnolia flowers around campus has been capturing my attention over the last few weeks, but it turns out they’re just as noteworthy for their therapeutic potential as for their aesthetics. A new article in press for PLoS One (open access for everyone!) describes a novel activity for the Magnolia officinalis derivative magnolol in repressing inflammation, which is a pretty tantalizing topic for a runner like me who’s always a little bit neurotic about the health of her joints.

Flowers of Magnolia x soulangiana, a cross between M. lilliflora and M. deundata.

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Magnolia x soulangiana

The pink magnolia tree on the street outside our house has been cropped into a rather unfortunate blocky shape in an effort to keep it from obstructing the sidewalk.  Nevertheless, the buds it produces  this time of year are awfully pretty.  The mix of fuzzy, smooth, and knobbly textures on the sepals, petals, and twigs always makes me want to grab a pencil, so…

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Alliums: giving the immune system a smelly leg up

By February I am generally fed up with the cold and flu season, and this year is no exception.  Our household has been hit hard by a cold/bronchitis 1-2 punch, and we’ve been single-handedly keeping the makers of Ricola and our local Pho (Vietnamese chicken soup) shop financially solvent for the last few weeks.

It’s about this time that I start musing about zinc, antivirals, ICAM-1 inhibitors, VP4 protein based vaccines…in short, why the heck haven’t we found a way to beat the common cold?  Continue reading

Prettiest Plant in the Lab: Foxgloves, Digoxin, and Digoxigenin

A while ago I posted about oleander and the structural similarities between the oleander cardiac glycoside oleandrin and the foxglove cardiac glycoside digoxin.   But foxgloves express enough biologically useful (and harmful) molecules that they’re worth showcasing.  Plus they’re such nice eye-candy!

Gloves that pack a punch

The various members of the Digitalis genus, which include the gardener’s favorite foxglove Digitalis purpurea and a range of other Digitalis species, are favored ornamental plants for their tall showy flower spikes and bright colors.  A disputed but appealing origin for the name was advanced by William Henry Fox Talbot, who proposed that the whimsical ye Olde English people imagined fairies wearing the deep cone-shaped flowers for gloves, and called them folks’ gloves.  Very cute.  But given that fairies were famous not only for being adorable but also for other light-hearted mischiefs like stealing babies and poisoning livestock, it’s perhaps fitting that their pleasing-to-look-at gloves come barbed with a heavy dose of serious poison.

Enough folk's gloves for a children's book full of fairies. Digitalis purpurea, by Ferdinand Bauer.

Foxgloves are poisonous because they contain two cardiac glycosides, digoxin and digitoxin, which are found in all parts of the foxglove plant but are most concentrated in the leaves.  There are a few ways to poison yourself with foxgloves by mistake: the flowers have some appealing similarities to honeysuckle, which might lead the unwary to try to suck nectar from them.  Because the plant is still poisonous when dry, a hapless gardener might inadvertently inhale foxglove plant matter when digging or replanting near an old foxglove bed.  The leaves of foxglove (especially before it flowers) resemble and have sometimes been mistaken for comfrey, which is benign and a common basis for tea (here’s an article about several people poisoned this way).  Never fear though, ehow has a handy how-to on distinguishing comfrey from foxglove leaves; the clearest difference might be that foxglove leaves are finely toothed while comfrey’s are smooth.

Leaf of comfrey, Symphytum sps. Good for tea, beloved by herbalists, and pretty easy to confuse with foxglove leaves, pictured in the illustration above. Photo courtesy of Heather at, which is also a pretty nifty blog.

Finally, one of the side effects of digitalis poisoning is strong hallucinations, so there may be a handful of people out there ingesting it deliberately…but I doubt the visuals are worth the heart arrhythmias, severe nausea, fainting, coma and possible death that come with them.

Extra nitty-gritty: Digoxin as heart medicine

Cardiac glycosides like digoxin and oleandrin work as sodium-potassium ATPase inhibitors, which means that they interfere with the balance of ions inside cells. The muscle cells of the heart are particularly vulnerable to changes in sodium concentration, because sodium concentration is coupled to calcium export, and the calcium concentration inside the muscle cell is what regulates how strongly or quickly the muscle cell can contract.  When there’s too much sodium, the cell can’t efficiently export calcium, and the cell contracts too strongly as a result.  Erratic muscle contractions are certainly bad news for a healthy heart.

Digoxin: sometimes a help and sometimes a hindrance to heart function.

Unlike oleandrin however, digoxin has considerable utility as a medicine: the same calcium ion hoarding effect that’s so dangerous in a healthy person can be used to combat heart failure by promoting stronger contractions in a damaged heart, and digoxin gained FDA approval as a treatment for chronic heart failure and some kinds of heart arrythmias in 1998.

The initial use of digoxin came before beta-blockers were used to manage heart failure (HF), and there is ongoing study as to whether digoxin remains valuable as an HF management strategy in concert with other therapies. A recent article in the International Journal of Cardiology has undertaken a multivariable regression approach to attempt to classify which categories of patients are more likely to suffer higher mortality or further hospitalizations for heart failure following digoxin use.  Their meta-study combined cases of over 7000 patients, and found that higher mortality and hospitalizations for heart failure were correlated with groups of patients that were female and had high blood pressure.  Studies like this one may help identify which groups of patients can still benefit from digoxin and which groups should avoid it.

Extra nitty-gritty II: Digoxigenin as molecular label

Apart from its cardiac glycosides, Digitalis also harbors a supremely handy steroid, Digoxigenin (DIG), which I use routinely to label RNA molecules.  Digoxigenin is a fairly small little molecule that can be coupled to the nucleotides that make up DNA or RNA (nucleotides=letters: A,G,T/U, and C), and there are specific antibodies for DIG that can be used to detect it anywhere it’s bound in a cell.

DIG-UTP. This labeled "U" is incorporated into RNA molecules just like regular UTP.

So when I want to find which cells in my tissue sample are making a certain RNA, I can make a probe with a complementary sequence and some of the U’s labeled with DIG.  Then I can use anti-DIG antibodies (conjugated to an enzyme that makes a purple color under the right conditions) to look for the probe, with a technique called in situ hybridization.

A little how-to for using DIG-labeled UTP to find a target RNA by in situ hybridization.

Want more details?  Here are references for the articles mentioned:

Ather S, Peterson LE, Divakaran VG, Deswal A, Ramasubbu K, Giorgberidze I, Blaustein A, Wehrens XH, Mann DL, & Bozkurt B (2011). Digoxin treatment in heart failure – unveiling risk by cluster analysis of DIG data. International journal of cardiology, 150 (3), 264-9 PMID: 20471706
Lin, C., Yang, C., Phua, D., Deng, J., & Lu, L. (2010). An Outbreak of Foxglove Leaf Poisoning Journal of the Chinese Medical Association, 73 (2), 97-100 DOI: 10.1016/S1726-4901(10)70009-5

Poppies part deux: taxonomical embarrassment

Botanical illustrators go crazy for poppies, so when I was looking for pictures to put in Monday’s post, there was one particular botanical illustration of Papaver somniferum I was looking for–one I’ve seen in maybe a dozen places, so I thought it must be the iconic, quintessential opium poppy illustration.  And I spent like half an hour on Google images, digging through variations on “Papaver somniferum red,” Papaver somniferum botanical,” Papaver somniferum painting…drawing…red…poppy…opium poppy red…opium poppy drawing….aaaarrggghhh!  Couldn’t find it anywhere.

But! I knew I had it in one of my botanical books at home.  So once I got back, I pulled out my copy of Wilfrid Blunt’s “The Illustrated Herbal,” found “poppy” in the index, turned the page, and cried out to JMG: “Ha!  See!  It’s right here, by Rinio!  Why was this not findable in Google?? Everybody loves this painting, it’s like the perfect painting of an…oh.  OOOOOhhhh.  It’s a corn poppy.  Well, dammit.”

Rinio's "Papaver rhoeas," the corn poppy. Not an opium poppy, it turns out.

Corn poppies are the ones from the poem “Flander’s fields” (the WWI poem you may have been forced to memorize in high school).  They grow wild in much of Europe.  And while the deep evolutionary conservation of alkaloid biosynthesis machinery in the Papaveraceae means they probably make a bit of the opiates their sibling species is known for, it doesn’t count as an opium poppy.  Hrmph.

In my defense, they look awfully darn similar.  As far as I can tell the main differences are the anther distribution and color in the center of the flower, and the size and roundedness of the seed capsule.  The foliage looks more feathery in the corn poppy too, but I think this varies among subtypes of the two species.

Why I am not a taxonomist: Opium poppies, Papaver somniferum, var "cherry glow" for purchase from Capital Gardens in the UK.

Lavender at the lab

If Stanford isn’t running a bustling underground soap and sachet business, it should be.

The grounds near the med school have stands of lavender large enough to comfortably carpet my entire house (ok, granted my house is the size of some people’s bedrooms, but that is not the point.  The point is that there’s a lot of lavender).

A mere sampling of all the lavender that populates our section of campus. It's listed as Lavandula "var," which seems only fair since apparently fighting over Lavandula species and subspecies names is a popular botanical pastime.

This hardworking Mediterranean mountain native is probably most famous for its use in bath oils, soaps, and fragrances (its name, after all, comes from the Latin lavare: “to wash”), but I like it best as a food flavoring—it’s great with chicken (see recipe, below), but also chocolate and other dessert items.

A closer look at the flower spikes

Extra nitty gritty:

The fragrance we associate with lavender in its essential oil comes from several compounds, mainly terpenes, but the biggest single component is probably linalool.  Linalool is made by a diverse array of sweet-smelling plants, including many others of the mint family to which Lavandula belongs.

linalool by any other name woud almost certainly still smell as sweet

Lately, the commercial and therapeutic utility of lavender has driven a more molecular approach to its cultivation, with scientists characterizing the expression levels of genes contributing to the biosysnthesis of linalool and other terpenes.  By studying how Lavandula angustifolia regulates production of its essential oil normally, new cultivars could be developed with greater essential oil output, and even more of a fragrant pop.

Interested in the details?  Here’s the reference:

Lane A, Boecklemann A, Woronuk GN, Sarker L, Mahmoud SS.  A genomics resource for investigating regulation of essential oil production in Lavandula angustifolia. Planta. 2010 Mar;231(4):835-45.

 And you can eat it!

So here’s my favorite lavender recipe, does anyone have a favorite of their own? Post a comment or a link–I’d love more!

Lavender chicken recipe:

4 Boneless Chicken Breasts

3 Tbsp Butter

1 clove garlic, chopped

1 large shallot, chopped

3-4 spikes lavender flowers (plus a few more for garnish)

1/2 cup pinot grigio or sauvignon blanc (we avoid chardonnay for cooking because the oak taste becomes too strong when the wine reduces)

1 tsp. Fines Herbes ( or a mix of marjoram, thyme, rosemary and a bay leaf or two works well)

2 Tbsp honey (clover or wildflower. Don’t use orange blossom; it turns out yucky)

juice of 1/2 lemon

Salt, pepper

Pat the chicken dry and rub with 1-2 Tbsp butter (or olive oil if that’s more your style), then sprinkle with salt and pepper.  Place so they fit fairly snugly in a baking dish.

Saute the garlic and shallot together in the remaining butter just until the shallot turns soft.  Then add wine, lavender, herbs, honey, and lemon juice and bring to a simmer.  Let simmer, stirring occasionally, until slightly reduced—about 5-10 minutes.  Slosh the resulting sauce over the chicken breasts and cook at 375 for 45-50 minutes, basting occasionally toward the end.  If needed, broil 4-5 minutes to brown chicken nicely.

Garnish with lavender and serve with the rest of the wine.  A big chunk of crusty bread is handy for sopping up the extra sauce.

Lavender chicken, my favorite brassicate, fresh-baked bread and a generous glass of sauvignon blanc. Dinner!