Thursday, 23 June 2011

Not tonight Josephine.

Apparently Napoleon never said "Not tonight Josephine", but it's probably the one thing most people associate with his wife, the Empress Josephine of France (1763–1814).
She should be more widely known instead for having this spectacular climbing plant named in her honour:
Copihue, Lapageria rosea
The Empress was born Josephine Tascher de la Pagerie, and it's from her surname that Lapageria is derived.
Lapageria rosea is the only species, and it's the national flower of Chile, which is where it occurs naturally.  I've been watching this plant in Kelburn, since noting its spectacular flowers.  The flowers are clearly monocot flowers—they have sepals and petals in threes—but take a look at the leaves:
Lapageria leaf, and note the Agapanthus leaf behind, a more typical monocot.

Monocots are supposed to have parallel leaf veins, and these are clearly reticulate (net-like), which is generally characteristic of eudicots and basal angiosperms.  What's going on here?
Judd et al. (2008) explain: "Several monocots have pinnate to palmate leaves with obviously reticulate venation patterns ..., but these are probably reversals associated with life in shaded forest understory habitats".  How do they know this?
There are two possible ways that some monocots could have net-like leaf veins.  First, the groups with net-like veins could be at the base of the monocot family tree, and then we'd interpret their venation as an ancestral dicot-like feature that they've retained. 
Alternatively, they could be derived higher in the family tree of monocots, from ancestors that had parallel veins, in which case we'd infer that there was a shift from net-like to parallel at the base of the monocots, followed by a reversal to net-like higher in the tree.
When we look at a family tree (a phylogeny) of the monocots, it's clear that the second interpretation is the correct one, because these net-veined plants are deeply nested among species with parallel venation.  Indeed, it seems this reversal has happened more than once.  Lapageria is classified in family Philesiaceae among the Order Liliales.  Some other net-veined monocots are also placed in Liliales, such as our native Luzuriaga (Alstroemeriaceae) and supplejack, Ripogonum  (Ripogonaceae).  But net-veined Dioscorea (the true yam, not to be confused with oca, Oxalis tuberosa) is classified in Dioscoreales, so it looks as if they came by their net-veined leaves as a separate event.
Luzuriaga parviflora
It seems the genetic ability to make net-veined leaves might be present in many monocots but silenced in some way, making it relatively easy for reversals to evolve.  There are several well-known mechanisms for this kind of evolution.  (Added 8 July 2011: Here's a great description of how this kind of thing can work)
Lapageria rosea (local name copihue) is the national flower of Chile.  Hanging red flowers from South America, with no landing place for a pollinating bird, are characteristic of hummingbird pollination.  Sadly, we have no hummingbirds in New Zealand.  The plant I've been watching does set fruit, but the fruits seem to fall before the seeds are ripe and it may be that fruits begin to develop even when the flowers haven't been pollinated.  The anthers are close to the stigma, so you'd think it could self-pollinate, but maybe some other mechanism is preventing seed set.  I might put on my bumble-bee suit and try pollinating it by hand.
Inside the flower, showing the 6 anthers close to the stigma.

Judd, WS; Campbell, CS; Kellogg, EA; Stevens, PF; Donoghue, MJ (2008).  Plant systematics a phylogenetic approach (3rd ed.).  Sinauer, Sunderland MA.

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