Fruiting karaka

Karaka (Corynocarpus laevigatus) is a small New Zealand tree with large fleshy fruits.  It's interesting for a number of reasons.  Its fruits were an important food resource for Māori but the kernels had to be treated to remove the toxins they contain.  It's become a weed in some parts of the world. Some botanists consider it a weed within New Zealand too, when it becomes invasive outside its presumed native range or habitats.

Right now, karaka trees are fruiting heavily.  But not all of them.  Some trees are covered in fruit and others have none or very few.  Some years ago, I wondered if this meant they had separate sexes, and was able to show that this is the explanation (Garnock-Jones et al. 2007).  Male trees do produce a few fruits, so the sexual system in karaka is best described as gynodioecy (some plants strictly female; others are inconstant males).

Here are the two trees that started this research off, photographed this month in Kelburn.

Karaka trees in fruit, Kelburn, Wellington, 2014

Here are the same two trees about 10 years ago.

Karaka trees in fruit, Kelburn, Wellington, 1998 (from Garnock-Jones et al., 2007)

On the female tree, the panicles fruit heavily, with many of the flowers (but by no means all) developing fruits.

Fruits on a female karaka tree

On males, usually a single fruit develops on each of a few panicles.

Fruits on a male karaka tree

Karaka flowers are small and white, but if you look closely you can tell the male from the female flowers.  The male flowers are actually about twice the diameter of females, open more widely, and have pollen in their anthers.  The male flowers in the photo have pollen on the stigmas, but only very few of them will produce fruits.

Karaka flowers.  On a female tree (left); male tree (right)

Reference.

Garnock-Jones PJ, Brockie RE, FitzJohn RG 2007.  Gynodioecy, sexual dimorphism and erratic fruiting in Corynocarpus laevigatus (Corynocarpaceae).  Australian Journal of Botany 55: 803–808.

Wednesday wildflower: miner's lettuce

Claytonia perfoliata, basal leaves

Miner's lettuce, Claytonia perfoliata, is wild foragers' fare.  Its succulent leaves can be lightly steamed or eaten fresh in a salad.  The plants are annual, and I first noticed the seedlings about 6 weeks ago.  Lately there have been a few early flowers.

The little white flowers form in clusters in the centre of roughly circular bracts.  Each flower has two sepals, five petals, five stamens, and three stigmas on top of the ovary.  The flower stalks elongate as the flowers get older.  The seeds are small, shiny, and black.

Claytonia perfoliata.  Basal leaves, A, adaxial, B. abaxial; C. perfoliate bract with flowers; D inflorescence and side view of flowers, showing the paired sepals.

The genetic revolution in classification has affected few plants more than it's affected miner's lettuce and its relatives.  It used to be classified with Portulaca in the Portulacaceae.  It was a big surprise to discover that the cactus family arose within that lineage, and this brought about the suggestion that the two families should be combined.  However, more recently, an alternative has been proposed: the Portulacaceae can be broken up into a number of smaller families that can sit alongside Cactaceae.  One of these is the now very much smaller version of Portulacaceae (New Zealand has a couple of naturalised species of Portulaca), but miner's lettuce and some other naturalised and native New Zealand plants ended up in the Montiaceae.  I'll certainly cover Calandrinia menziesii and Montia fontana as future Wednesday Wildflowers if I get suitable material, but for now here are some native species in Montiaceae.

Montia australasica, a common and variable alpine species found in New Zealand and Australia, at Rastus Burn, Remarkables Range, Otago.  Some botanists prefer to divide it into at least 7 species.

Montia fontana subsp. fontana is a native aquatic, here growing in a stream at Sandy Bay, Enderby Island.  M. fontana subsp. chondrosperma seems introduced, and grows on soil.

Hectorella caespitosa, here at Rastus Burn, Remarkables Range, Otago, used to be classified with its close relative Lyallia kerguelenensis (from Kerguelen Island) in its own family, Hectorellaceae.  Now their relationships are better known, they're placed in Montiaceae.  Some argue the two should be in the same genus (Lyallia caespitosa would then be the name for our species).