Tuesday, 28 August 2012

Wednesday wildflower: groundsel.

When I was young, about 11 or 12 I guess, I caught a budgie on the neighbor's front lawn.  I spotted him through the kitchen window, a flash of brilliant blue struggling against the Wellington wind.  When he settled on the lawn I ran over there and flung my tee shirt over him, and carefully carried him home.  We tried to find his owner, but eventually we gave up and Bluey became part of our household.  I never managed to teach him to talk, but he did have a cheerful whistle.

The neighbors told me to hang a sprig of groundsel in his cage, so I'm pretty sure groundsel was one of the first weeds I ever learned the name for.  I scoured the garden for it, and even today I always notice groundsel, even though it must be 45 years since Bluey died.
Senecio vulgaris leaves (A, abaxial; B, adaxial) and flower heads at flowering (C), early fruiting (D) and after fruiting (E).
Groundsel, Senecio vulgaris, is a common weed of cultivated ground.  The flower heads lack ray florets, but are otherwise similar to other senecioids, like Roldana.  The loss of rays and the smaller stigmas in S. vulgaris suggest self-pollination, but the mating system seems not at all straight-forward.  Some plants in Europe do produce rays, but New Zealand populations of S. vulgaris are reported to be all rayless (Webb et al., 1988).  Ray production is controlled by a group of regulatory genes, which are expressed (or not) in the outer florets of a head (Kim et al., 2008).  In conditions where self-pollination is advantageous, raylessness is favoured.

References.

Kim, M; Cui, M.-L.; Cubas, P.; Gillies, A.; Lee, K.; Chapman, M.A.; Abbott, R.J.; Coen, E. 2008: Regulatory genes control a key morphological and ecological trait transferred between species.  Science 322: 1116–1119.

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

Friday, 24 August 2012

Banana seeds

Banana fruits are classified botanically as berries (fleshy fruits with many seeds).  Also the plants are botanically herbs because they don't have a woody stem; their "trunks" are made up of overlapping tubular leaf bases.  The fruits of the commercial varieties are seedless, and just as well too.  This works because the plants can be propagated vegetatively.  However their "unfortunate sex life" means there's little genetic variation in the cultivated stocks, so bananas are always at risk of being wiped out by a crippling disease.

Those little brownish dots inside a banana are the ovules, not seeds.   

These are the seeds:
Banana seeds, from a plant cultivated at Paekākāriki; scale 10mm long.

They're big and hard; you wouldn't want to bite down firmly on one of these.  (Thanks Joe, for bringing these in.)

Tuesday, 21 August 2012

Wednesday wildflower: brush wattle

Brush wattle, Paraserianthes lophantha, is a common small tree that's weedy in many parts of New Zealand's North Island and some milder parts of the South Island and Stewart Island.
Brush wattle growing in a gully in Kelburn, Wellington, with Teline stenopetala (yellow flowers, foreground) and ngaio (Myoporum laetum, rounded shrubs, background).
It's a fast-growing tree and can spread rapidly by seed in waste places like gullies and roadsides.
Paraserianthes lophantha.  A, leaves (adaxial on left, abaxial on right); B, an inflorescence; C, a developing pod, with the corolla somewhat enlarged and the stamens withered; D, leaflets, adaxial on left, abaxial on right; E, gland on the leaf stalk; F, flower buds; G individual flowers.
The compound leaves have a conspicuous gland on the leaf stalk (E above).  Brush wattle flowers are clustered together to form a brush blossom (B above).  Later in the season these will be clusters of dry brown pods.

Thursday, 16 August 2012

Friday Fungus: basket fungus

The basket fungus, Ileodictyon cibarium, is commonly found in gardens, especially following mulching.  Ridley & Horne (2006) reckon it's become much more common over the last three decades as mulching has become popular.  This one was under kānuka (Kunzea ericoides) in the Wellington Botanic Garden.

It's Māori name is tūtae kēhua (ghost droppings) or tūtae whatitiri (whatitiri is thunder, so this might allude to the fungus appearing after storms).  The spores are presented in a brown smelly secretion at the base of the basket, which gets smeared around the basket and attracts flies.  The basket sits fully-formed inside the "egg" and can wait out a dry spell to erupt suddenly after rain. The sudden appearance of these would be quite dramatic, ghostly even.  The basket isn't attached to the "egg", so it can blow or roll about, dispersing spores.

Reference

Ridley, G.; Horne, D. 2006.  Mushrooms and other fungi of New Zealand.  New Holland Publishers.

Tuesday, 14 August 2012

Wednesday wildflower: spurrey

Spurrey, Spergula arvensis, Kelburn, Wellington, New Zealand.
Caryophyllaceae is a large and diverse family of flowering plants, with 70 genera and 2200 species (Judd et al. 2088).  Annoyingly, a lot of the names of the genera start with S: Silene, Spergula, Spergularia, Stellaria, Scleranthus, Sagina, and Saponaria.  This week's wildflower, spurrey (Spergula arvensis), is a common garden weed in New Zealand.  It's native to Europe and has been here in New Zealand since 1855 (Webb et al. 1988).
Spergula arvensis.  A, B, nodes and leaf bases, showing pale pinkish triangular stipules (circled); C, an inflorescence; D, bud and open flowers, the latter with two anthers missing.
The leaves are in opposite pairs, but each leaf sports a branch with suppressed internodes, making what appears to be a whorl of leaves at each node (A above). There's a broadly triangular membranous stipule between the leaves of a pair on each side of the stem (circled in B above), which sometimes drops off (A above).
  
I noticed something interesting when I was preparing the images.  The plant was in full flower when I collected it, but the flowers closed in the semi-shade of my office.  I resigned myself to not having open flowers to illustrate this post.  However, the light from a single pass of the flatbed scanner on an inflorescence with closed flowers (C in the picture above) seemed to be enough to open them again quite quickly (bottom right, above).  I'll follow this observation up soon.

References
Judd, W.S.; Campbell, C.S.; Kellogg, E.A.; Stevens, P.F.; Donoghue, M.J. 2008: Plant systematics a phylogenetic approach. Sinauer, Sunderland, Massachusetts.
Webb, C. J.; Sykes, W. R.; Garnock-Jones, P. J. 1988: Flora of New Zealand. Vol. IV. Christchurch, Botany Division DSIR.

Saturday, 11 August 2012

Plant play: Snapdragons

Snapdragons (Antirrhinum majus) are hours (well minutes) of fun.  Hold the flower by the sides of the tube and squeeze:
video

There's some interesting botany behind this.  Flowers can be well-adapted for particular pollinators.  But often that doesn't stop other visitors entering the flower and stealing nectar or pollen without effectively pollinating it.  Some flowers have a palate that closes the corolla throat so that only a pretty strong insect can force its way inside.  Snapdragons have this strategy, as do some of their relatives, like ivy-leaved toadflax and Linaria.

Tuesday, 7 August 2012

Wednesday wildflower: velvet groundsel, Roldana petasitis


The Asteraceae is a huge family (1535 genera/23,000 species, according to Judd et al. 2008) and Senecio is the largest genus, with 1250 species.  That's after some smaller genera have been segregated, like the mostly New Zealand genus Brachyglottis and the American genus Roldana.
The Asteraceae is characterised by having compound blossoms (capitula or heads) made up of many small florets.  In some, these heads are homomorphic, with just one type of floret (e.g., dandelions and thistles), but in most they're heteromorphic and have both ray florets and disk florets.  In some groups that normally have heteromorphic heads the ray florets may be lost to make a heteromorphic head; that seems to happen readily in some species of the Senecio tribe, Senecioneae.  Outside of the ray florets are the green involucral bracts, which in Senecio and its relatives are characteristically in one non-overlapping main row (D in the plate below).
Roldana petasitis, Kelburn, Wellington.
Today's wildflower is a species that's introduced to New Zealand and established mostly in parts of the North Island, probably as a garden escape.  The plants are softly woody shrubs, up to 2 or 3m tall.  These ones were collected in the Norway Street area of Kelburn, Wellington.  It's native to Mexico, but probably came here via Britain, where it is cultivated at least in the south, or perhaps via USA or Australia.
Roldana petasitis, an inflorescence of capitula.
The Flora of New Zealand (Webb et al. 1988, as Senecio petasitis) says it establishes locally from garden discards and from seed, and certainly this population looks like it has spread by seed to places where garden discards seem unlikely.  Yet the Flora doesn't describe the fruits, so I assume there were none available for study.  I'll be keeping an eye on these plants as the season progresses to see if fruits are produced.  The New Zealand Plant ConservationNetwork website says seeds are the main means of spread.  (Technically, in Asteraceae, seeds are dispersed inside 1-seeded fruits, called cypselas.)
Roldana petasitis, leaf.
The leaves are large, up to 20 cm diameter; the one in the plate below is a small one from just below the inflorescence.
The heads are produced in large branching inflorescences.  At first the five (occasionally 4 or 6) ray florets open and expand.  Then the outer disk florets begin to shed pollen.  In this male phase the stigma is pushing the pollen out through the anther tube, where it's presented between the projecting awns of the anthers (which are visible in the centre of D below).  Later, when the pollen has gone, the two arms of the stigmas open, ready to receive pollen.
Individual florets are also shown (C below), two rays on the left and three disk florets on the right.  The rays are female (they have no anthers) whereas the disk florets are hermaphrodite.
Roldana petasitis.  A, small upper leaf, adaxial surface; B, the same, abaxial surface; C, florets, two rays (left) and three disk florets (right); D, a capitulum, showing ray and disk florets and involucral bracts; E, a series of capitula at increasing time from first opening (see text for description); F, details of leaf surfaces, adaxial (left and abaxial (right).
Senecio has been a taxonomic problem for decades.  Most people regarded the genus as too big to make sense, but in the past it's been hard to achieve consensus among botanists about the various attempts to break it up.  Recently, the application of cladistic (tree) thinking and molecular data to this problem genus has yielded good results that seem to fit with morphology and biogeography (e.g., Pelser et al. 2007).  There's now good reason to treat this species as a member of Roldana, rather than Senecio.
References
Judd, W.S.; Campbell, C.S.; Kellogg, E.A.; Stevens, P.F.; Donoghue, M.J. 2008: Plant systematics a phylogenetic approach. Sinauer, Sunderland, Massachusetts.
Pelser, P.B.; Nordenstam, B.; Kadereit, J.W.; Watson, L.E. 2007 An ITS phylogeny of tribe Senecioneae (Asteraceae) and a new delimitation of Senecio L. Taxon 56: 1077–1104.
Webb, C. J.; Sykes, W. R.; Garnock-Jones, P. J. 1988: Flora of New Zealand. Vol. IV. Christchurch, Botany Division DSIR.

Friday, 3 August 2012

Gametophytes

You might not believe it if you haven't studied botany (you might not believe it even if you have), but these are mature, fully grown, reproductive ferns.
Fern gametophytes.  I guess these might be Pneumatopteris pennigera, because that's what they were growing under.
All land plants have two multicellular stages in their life cycles, but in seed plants, one of the stages is so small that we can't see it without a microscope.  Ferns are good for demonstrating this alternation of generations because both life cycle stages are big enough to see with the naked eye.

The little heart-shaped plants above are fern gametophytes.  A familiar, big, leafy fern plant (it's called the sporophyte phase) produces spores in thousands of little structures—sporangia—underneath its leaves, and the spores don't grow into new leafy ferns, but into these little gametophytes.  Gametophytes in turn produce gametes (eggs and sperms), and when a sperm fertilizes an egg a new sporophyte fern is born.
Fern gametophyte, lower surface showing the notch and the tuft of rhizoids.
Fern gametophytes are delicate, thin sheets of plant tissue that are confined to damp places.  New growth arises in the notch of heart-shaped gametophytes like this one, where tiny cells are actively dividing.
The small actively dividing cells of the notch form the growth point of the gametophyte.
The gametophyte is anchored to the ground by a tuft of rhizoids (they're not roots: they don't take up water and they have a very simple structure).  Just back of the notch and among the rhizoids, the sexual structures form.  Some of these—archegonia—are female and each makes an egg.  Others—antheridia—are male, and each makes numerous sperms.  The sperms swim through a film of water, and find eggs following a chemical (often a sugar like malose) that diffuses from the archegonia.
Archegonia (circled).  They're very hard to photograph with just a dissecting microscope and a hand held camera.
One of the joys of teaching botany is you get to see (over and over again) some of the strange and wonderful aspects of the plant world.  Before I taught, I'd always thought gametophytes would be almost impossible to find—after all, the seedless plants are called cryptogams, which refers to their hidden sex lives.  But gametophytes aren't hard to find.  Look for a damp bank under overhanging fern sporophytes.  The gametophytes are often among mosses and can be hard to see at first.  It's easiest to look for tiny fern sporophytes that are just emerging between the lobes of the gametophytes (there's one overlapping the edge of the coin below); when these are small enough, the gametophytes they grew from haven't yet shriveled. Once you get used to what you're looking for, you'll find they're pretty common.

Occasionally you can strike it lucky.  This freshly-cut bank (below) was almost entirely covered by fern gametophytes, in many the eggs had been fertilized and young sporophytes were just emerging.
Fern gametophytes, those on the right with young sporophytes emerging.
You can grow your own too.  You'll need some peat in a pot, and it's not a bad idea to sterilize it first (I guess a microwave would be a simple way to do this at home).  Collect a leaf from a fern you want to grow (check it's got sporangia underneath), and let it dry out in a paper bag so the spores are shed.  Scatter the spores (fine brown or yellow dust) onto the surface of the thoroughly moistened peat, and cover the pot with a sheet of glass or a plastic bag, to keep the moisture in and other spores out.  Exposed to sunlight (not too strong), the spores should germinate to produce a dense crop of gametophytes, and if you wait long enough and keep them moist, they should produce little sporophytes that you can plant out.