Wednesday wildflower: Cape weed

Here's something to watch for if you like foraging for wild food: be very careful about misidentifications.  I remember visiting someone in Christchurch once who was carefully transplanting wild hemlock (this one) seedlings into her herb garden, thinking they were angelica.  Well, I shouldn't be smug about that, because yesterday I made a mistake that could have had nasty consequences if I'd been foraging and if the mistake had been in the reverse direction, but I like to think I wouldn't have made it if I'd had a fresh plant or a dried specimen, rather than a photo, to identify.

It was on the Naturewatch website, and someone had posted a photo with a request for identification.  I thought it looked like puha (Sonchus oleraceus), but then I changed my mind and identified it as Cape weed, Arctotheca calendula.  The great thing about Naturewatch is that the identifications are crowd-sourced, and others quickly challenged my identification and convinced me, with evidence, that I was wrong.  The plant was indeed puha (Sonchus oleraceus).  (It's a bit embarrassing, because I wrote the Flora of New Zealand treatment for both these plants.)

So yesterday, I went looking for some fresh material.  Here are the upper surfaces of the leaves:

Cape weed (left) and puha, upper surfaces (scale=1cm)

And here are the lower surfaces.

Cape weed (left) and puha, lower surfaces (scale=1cm)

The Cape weed has more leaflets, a rounded, rather than triangular terminal leaflet, bristly hairs on the upper surface and a dense silvery mat of hairs below (puha leaves are hairless except for bristles at the tips of the teeth on the upper leaves).  Cape weed's leaf stalk is also bristly compared to the smooth puha.

Of course, it'd be hard to confuse them in flower, but early growth is often the time when foragers collect, because some plants get bitter when they run to flower.

Cape weed (left) and puha in flower.

Cape weed is poisonous, but not very, whereas puha is edible.  Check out Johanna Knox's foraging website for information, and always be sure you identify your target.

The moral of the story is that identifying plants from photos can be difficult.  Often the diagnostic characteristics can't be seen and sometimes the colours recorded in a photo don't look the same as in life.  Plant taxonomists (specialists in the classification, naming, identification, and evolution of plants) often refuse to identify photos, but I believe that so long as people understand the pitfalls it's worth having a try.  I really like the Naturewatch site, because it's self-correcting, democratic (everyone can have a go), and we all learn something from participating.

Wednesday Wildflower: Brazilian pepper tree

I've been wondering about some trees in Sunnynook Park every time I visit Auckland.  From the shape of their leaves and their panicles of small flowers I had assumed they're something in the Cunoniaceae. But I should have been more curious and looked more closely, because these leaves are alternate, whereas Cunoniaceae have opposite leaves with interpetiolar stipules.

Schinus terebinthifolius, a flowering branchlet from a female tree.

This week I was there again and saw one of the trees had little round pinkish fruits, and I realised this is Schinus terebinthifolius.  I knew S. molle, which has more graceful hanging leaves, and I knew the fruits of S. terebinthifolius are the pink peppercorns you sometimes see mixed with black peppercorns (Piper nigrum) in pepper grinders. (Pink pepper, confusingly, is made with true black peppercorns, using newly-ripened berries and treating them with brine and vinegar, described by McGee, 2004.)

It's becoming a bit of a problem weed in New Zealand and worrying some weed experts.  Back in 1988, Flora of New Zealand Vol. 4 didn't record it as naturalised (Webb et al. 1988), but now it seems to be establishing.  It's a major weed in many warmer countries.  The trees in Sunnynook Park don't seem to be spreading, although there appear to be suckers coming up from the roots.  Most of the trees there are male, but I did spot a couple of females.

It seems a lot of our new weeds are woody, and many are bird-dispersed.  I wonder how many originate from more tropical climates and owe their success here to climate change.

The Flora says it has 5–9 leaflets.  The leaf I randomly chose to photograph had 11:

Schinus terebinthifolius leaf

That doesn't mean the identification is wrong.  Many characteristics of plants are more variable than the descriptions cover, partly because the descriptions are based on a smallish sample that doesn't allow for the odd extreme.

Pink pepper is in the family Anacardiaceae, the same family as mango, cashew, and poison ivy; some people are very allergic to this family.  According to McGee (2004) it owes its peppery flavour to cardanol, an irritating phenolic compound.

References.

McGee, H. 2004.  On food and cooking, the science and lore of the kitchen. (Revised edition), Scribner.

Webb, C.J.; Sykes, W.R.; Garnock-Jones, P.J. 1988.  Flora of New Zealand Vol. 4.  Botany Division, DSIR.

Marmalade

I made marmalade today, something I’ve never done before.  I used mandarins from Johanna Knox’s garden.  Marmalade is citrus jam and the word marmalade comes to us from the Greek melimelon (a quince jam made with honey; the Greeks didn’t have cane sugar) via Portuguese.

Clockwise from top left: mandarin, navel orange, lime, lemon.

Citrus is a genus in the family Rutaceae, and the particular kind of fruit they have is a hesperidium.  Slice it cross-wise and you’ll see radiating walls like the spokes of a wheel; these are the walls of the individual carpels that make up the ovary and fruit.  Outside the carpels is the rind, made up from the ovary wall.  The rind is rich in flavorsome oils, which will burn dramatically if you squeeze lemon peel next to a lighted match. 

The inside of each locule (cavity) is packed with juice-filled hairs, and a few seeds along the central core of the fruit.  Each of those juice-filled bags within a carpel contains lots of juice-filled cells, and the cell walls have a special role in the making of marmalade.

Sliced lemon, showing 8 carpels, pith, and rind.

I’m indebted to a wonderful book for much of what follows: On food and cooking, by Harold McGee.  I have the 2004 edition.  I can’t recommend this book highly enough: food, botany, and chemistry—who could ask for more!

Plant cells are enclosed in relatively rigid cell walls made of cellulose.  Each cell secretes its own cell wall, by transporting vesicles of cellulose to be extruded through the cell membrane. The individual cells are stuck together by a thin layer of pectin, the middle lamella.  Pectin is an essential ingredient for marmalade, because it makes the gel that gives solidity to the jam. 

Pectin is a polysaccharide, a long chain of sugar molecules joined end-to-end.  The pectin chains are attracted to each other and form the glue that binds the cells tightly together.  But when fruit pulp is boiled in water, the pectin strands separate and they can’t come back together to find each other among all that water.  So the first step in making marmalade is to boil up the fruit in water.  I boiled mine for 2 hours.

Once the pectin is boiled out of the middle lamellae into solution, the jam-maker has to reassemble the pectin gel to set the jam.  Three properties of pectin are useful here.  First, adding sugar to the solution gives the pectin molecules something to coalesce around; they’re attracted to the sugar molecules.  Secondly, an acid environment helps the pectin gel to form.  I beefed up the acidity by adding the juice of a couple of lemons.  Thirdly some of the water has boiled off by now, and more will boil off from the sugar solution because adding sugar raises the boiling point to about 110C.  When these conditions are right, the pectin forms a gel as the solution cools, trapping water in the network of pectin strands: marmalade.

Four and a half jars of Theobrominated marmalade.

My marmalade turned out pretty cloudy, because I got lazy and simply put all the fruit through the food processor to make a pulp; then I sieved a lot, but by no means all, of the solids out of it. The left-over pulp will be great stuff for cleaning the glass of the shower; citrus juice is so acid that it’ll dissolve the scale (calcium carbonate) that forms as water dries on the glass.   The marmalade also set pretty solid; perhaps I over-sugared it.  

Puha

Before European contact brought a wealth of Eurasian and American temperate crops to New Zealand, Maori had to find their food among the native flora and fauna and the few crop plants they brought with them from the tropical Pacific.  New Zealand lowland plants are often woody and there are not many suitable green vegetables.  One of the best is puha, sometimes spelled puwha.

Puha seedling

Puha is classified in the genus Sonchus, which is part of the daisy family Asteraceae.  Within Asteraceae, puha belongs in the tribe Lactuceae, along with lettuce, dandelion, chicory, and salsify.  The name Lactuceae refers to the milky juice that's characteristic of this tribe.  This juice contains sesquiterpene lactones, whose bitter tastes probably protect the plants against grazing.  These have been reduced in commercial lettuce varieties by plant breeding.
Native species.

New Zealand has between three and five native species of Sonchus, plus three introduced ones.  Few New Zealand botanists would agree with me about the number of native species; most would say there's only one.  In fact, I'm the author of the most recent Flora treatment of Sonchus (in Webb et al., 1988) that says there's only one, so I'll explain the reasoning behind my change of heart. 

First, there's Sonchus kirkii, which was probably the original Maori puha.  It's a coastal plant with rather thick and glaucous (bluish-green) leaves.  The New Zealand Plant Conservation Network notes that it appears to be declining in abundance.

Sonchus grandifolius, cultivated at Otari–Wilton's Bush

Secondly, there's S. grandifolius, confined to the Chatham Islands.  It was separated from Sonchus by Egyptian botanist Loutfy Boulos in 1965 and placed in a new genus, Embergeria.  It differs from most Sonchus in being much larger in all its parts and lacking barbs on the pappus hairs at the tips of its fruits.  This is another of those cases of classifying plants separately if they're different from their close relatives.  However, large size and loss of adaptations for dispersal are common features of island plants worldwide, and I expressed doubt about this classification back in 1988.  Since then, molecular systematics (Kim et al. 2007) has shown S. grandifolius clearly is a member of the Sonchus lineage; to treat it as a separate genus would disguise its true relationships.

Finally, another 1–3 species should be added to New Zealand Sonchus.  The endemic genus Kirkianella was described in 1961 because the plant previously known as Crepis novae-zelandiae clearly didn't belong in Crepis.  In the 1980s I formed the view that it might rather belong in Sonchus.  I wish I'd said so at the time, because recent molecular systematics research has borne this out (Kim et al., 2007).  Its DNA sequences and its fluffy pappus are evidence of a close relationship to S. grandifolius.  It looks as if the great British botanists Bentham & Hooker came to the same conclusion; the International Plant Names Index lists Sonchus novae-zelandiae attributed to them, but I haven't checked it in the original yet to see if they formalised the name.  At the moment there's only a single species recognised in Kirkianella, but there are two different chromosome numbers and a range of leaf shapes, which are strong clues that there could be more than one species involved.

Introduced species.
Of the three introduced species, S. arvensis is a large creeping perennial with large flower heads and conspicuous yellow glandular hairs on the outer bracts.  It's known from a few locations in Hawke's Bay, Canterbury, and Otago. 

The two common wild species are S. asper and S. oleraceus.  S. asper is an annual or biennial with softly prickle-edged leaves and smooth fruits, whereas S. oleraceus is an annual with toothed leaves and wrinkly fruits.  

Puha, Sonchus oleraceus

 The name S. oleraceus gives it away as a plant that's good to eat, and this species has largely superseded S. kirkii as the edible puha.  Moreover, Kevin Gould and colleagues found it had antioxidant levels several times higher than blueberries (Gould et al. 2006).  But S. kirkii is said to be easy to grow from seed, so it'd be an interesting addition to the vege garden, and growing it could help conserve the species (but don't collect plants or seed from the wild; try a good native plant nursery).

So what's puha like to eat?  I have to admit I haven't tried it, and I'll instead refer you to Johanna Knox's blog "Wild Picnic" and her tempting recipe for puha pakoras at "Wild Concoctions".  Incidentally, the latter recipe featured recently on TV2's Erin Simpson Show, unfortunately without attribution, although it appears to be no longer on the show's website.  That's a serious breach of netiquette, or worse.