Tasmanian Plants

Leaves of the Fragrant Candlebush become 'incontinent' with age

There are more similarities between plants and humans than we give credit for. Introducing the concept of incontinence in plants!

Leaves are the key parts of a plant which carry out the important act of water exchange with the environment. This being so, how effectively a plant can use water depends on how the easily water vapour gets from inside the leaf through the cuticle (the covering cell layer on the surface of a leaf) to the outside.

Greg Jordan and Tim Brodribb of the School of Plant Science, University of Tasmania have been studying the physiology of plant leaves for some time now and in 2007 published a paper in the scientific journal Functional Plant Biology on an interesting finding that the leaves of Agastachys odorata (Frangrant Candlebush or White Waratah) actually become incontinent with age.

Agastachys odorata is an endemic plant of the Protea family (Proteaceae) and occurs commonly in the high rainfall western Tasmania. The leaves of A. odorata exhibit distinctive annual growth increments, making different aged leaves easy to tell apart. The leaves are also very long-lived, with evidence of some leaves remaining on plants for up to 21 years. This makes A. odorata a fabulous choice for studying plant water relations with regards to leaf age.

Greg and Tim wanted to test the hypothesis that water vapour leaks across plant cuticles more readily as plant leaves age. In A. odorata they found that the older leaves were less effective in controlling water loss and hence used water less effectively than younger leaves. The increasing permeability of the leaf cuticle is implicated as the cause for this but it is also likely that the ability to control stomata opening also decreases with age, much akin to poor urinary sphincter muscle control in sufferers of incontinence. Greg and Tim concluded that the decreasing ability to use water efficiently could be due to natural leaf damage that occurs throughout the life of the leaf.

When the leaves of A. odorata becomes too old, it is simply shed. After all, the plant has no lack of leaves to serve it’s physiological functions. If only humans had the luxury of replaceable urinary sphincter muscles.

I have deep respect for ferns living in harsh conditions and one such fern is  Asplenium obtusatum (Shore Spleenwort). This species is also present in New Zealand but the Tasmanian form is known as A. obtusatum subspecies northlandicum, a form that was described by the renown pteridoloist Pat Brownsey in 1977.

The Shore Spleenwort is allegedly common and grows on rocks along the coastline of Tasmania. Widespread as it is, I’ve only had the fortune of observing it growing on the cliff faces around the Remarkable Cave in the Tasman Peninsula and in the fernery of the Royal Tasmanian Botanical Gardens.

The fleshy and shiny fronds of this fern makes it instantly recognizable and reminds me of the Sea Spleenwort (Asplenium marinum) of the Northern Hemisphere, a fern I would very much like to meet. Being ferns of such similar habitats, I imagine some convergent evolution in form is at work here.

Asplenium obtusatum is tolerant of some salt spray, a remarkable feat indeed given the vulnerability of ferns during the earlier stage of their life cycle.

This earlier stage are known as the gametophyte phase, as opposed to the sporophyte phase that we call ‘ferns’. The gametophyte is an inconspicuous little liverwort-like a structure that germinates and develops from fern spores. In most botany textbooks the fern gametophyte is portrayed as a heart-shaped structure and is called the prothallus. It is from the prothallus that the male and female reproductive parts develop. When the time is ripe for fertilization, the sperm swims through a film of water to find an ‘egg’ to fertilize. From this union, a baby fern is born, growing out of the tissues of the prothallus. The cycle is complete.

Unlike flowering plants, the fertilization of ferns require a film of water as mentioned above. Imagine the physiological stresses that a fern prothallus has to endure when the occasional salt spray comes into the picture!

The Shore Spleenwort is indeed a hardy fern worthy of a lofty station by the magnificent cliffs of the Tasmania coast!

In Tasmania’s heaths, herbfields, cliffs, lake margins and among cushion plant communities of the Northwestern and Central highlands lurk one of Tasmania’s most elusive botanical secrets – a little lily that hails from a botanical lineage of great antiquity.

First though, we must clarify what exactly is a lily.

The natural history and taxonomic relationships within the large family of lilies (Liliaceae) often vexed botanists in the pre-molecular age. After botanists became well accustomed to assigning the appellation of ‘lily’ to a great many species of plants, the molecular blade swiftly and decisively ended the empire of the the lily family. Asparagus (Asparagus spp.), the onions (Allium spp.), the pineapple lilies (Astelia) etc.,  became allied to other plant Orders (as will be elaborated in another post!).

Some of the remaining members of what was once the Liliaceae still remain in what is considered an Order of Lilies, the Liliales. However, the members of this once colossal lily family grouped into smaller families of their own.

One family of lilies, the Campynemataceae, is of paramount interest. Molecular work based of the gene sequences of the RuBisCo enzyme (rbcL) that is present in the chloroplasts of all plants, tells us that the Campynemataceae lineage is the oldest among all that can still be considered a part of the great lily order. In 2004, researchers Thomas Janssen and Kårl Bremer compared the rbcL sequences of representatives of the families in the Lily Order and estimated the Campynemataceae lineage to have come into existence some 117 million years ago, as a sister group to all other families of the Lily Order.

The lily I have deemed to be one of Tasmania’s most elusive botanical secret is Campynema lineare (Green Mountainlily), a representative of the Campynemataceae.

C. lineare is endemic to Tasmania and is the only species in its genus, and Campynema is one of the two genera in the family. The only other members of this family is a genus of three species, the Campynemanthe, that hails from New Caledonia.

C. lineare is a slender herb up to almost half a meter in height, but usually much smaller in highland areas. The leaves are linear as the specific epithet ‘lineare‘ suggests’ but highly inconspicuous when the plant is not in flower. The blossoms are scarcely 2 cm across, with yellowish-greenish floral parts, borne on a brownish stem. This combination does not help in making it stand out well from the surround vegetation. Before releasing pollen however, the bright orange stamens do stand out quite clearly against the greenish floral parts, but in most other respects, C. lineare is a rather inconspicuous plant and not largely different from what anyone would call a ‘lily’.

A casual observer would not have guessed that it is a relict of ancient lilies. Probably not even Jacques Labillardière, the french botanist who described the genus in 1805, guessed that he was beholding a botanical gem.

But the time of awareness is nigh. In this digital and molecular age, inconspicuousness can no longer be an excuse for the lack of recognition suffered by this marvelous plant. It is time for the little Green Mountainlily to take it’s rightful place among the ranks of Tasmania’s iconic plants. Like the Delicate Laurel (Tetracarpaea tasmannica), we must sometimes know of the historical significance of such plants before we can truly appreciate their contribution to botanical heritage of this land we call Tasmania, a home to plant lineages of great antiquity.

Hybridization as a means of making new species is not an uncommon concept and hence it must be applicable to other species. I present a case using a Tasmanian example – the Olearia daisybushes.

Olearia is a large and conspicuous genus of shrubs in the sunflower or daisy family (Asteraceae) with some 23 species in Tasmania of which 8 are endemic to Tasmania (not counting subspecies).

Left: Geebung Daisybush (Olearia persoonioides); Right: Prickly Daisybush (Olearia pinifolia); Centre: Possible hybrid

Two of the endemic species are of interest in this post: Olearia persoonioides (Geebung Daisybush) and Olearia pinifolia (Prickly Daisybush). Both are common and largish daisybushes that grow in subalpine woodlands.

Whilst botanizing at various spots around the Central Highlands I stumbled upon the two species of daisybushes growing in close proximity in the understorey of a eucalypt woodland. They were both in full flower. At the same time I also noticed numerous specimens that looked like intermediates between the two.

While this intermediate specimen deserves much more detailed study, I have prepared a set of photographs and made a table of the characters comparing the two daisybush species with the intermediate specimen.

Many additional aspects of the morphology of the intermediate specimen deserves study. For example, the morphology of the flowers and fruits (achenes) needs to be examined in greater detail. Other studies like chromosome counts might also be helpful in determining the hybrid status of the intermediate specimen.

A trip to the herbarium is in the works!

The Blue Gum (Eucalyptus globulus), Tasmanian Waratah (Telopea truncata), Deciduous Beech (Nothofagus gunnii), Myrtle Beech (Nothofagus cunninghamii) and Pandani (Richea pandanifolia) are names that are often cited by plant enthusiasts and bushwalkers guidebooks as ‘must-sees’ of Tasmania.

But these five iconic plants, showy and famous as they are, must defer to THE ONE TRUE ICON plant that represents Tasmania — the Delicate Laurel (Tetracarpaea tasmannica). The popular portraiture of Tasmania’s botanical gems must be expanded to exalt the Delicate Laurel and to remedy it’s unfortunate oversight.

(Yes I am being evangelical).

The Delicate Laurel is by no means an uncommon plant. It occurs in wet forest or more often, subalpine shrubberies in the western mountains. The plant blends quite immaculately into the surrounding scrub and is not extremely prominent unless in flower, the erect flower stalks bearing small odd-looking white flowers with 4-5 oversized carpels (female parts). Without consciously looking for it however, Tetracarpaea would be quite easy to overlook whilst hiking pass the lush shrubbery vegetation. Once known however, the plant is easily recognizable by it’s thick leathery serrated leaves. The brown dry fruits (folicles) are also quite distinctive.

Distinctive as it is, the history of how the plant was named and classified has been fraught with difficulty and confusion (See Tasmanian Flora online profile).

The eminent botanist Joseph Dalton Hooker is often attributed with having named and described the plant in but it has only recently been clarified that it was his father, Sir William Jackson Hooker that had found and described the plant (The original illustration of the plant in Sir William Hooker’s Icones Platarum may be found here). It was also only recently that the correct species epithet ‘tasmannica‘ was reinstated, as opposed to the commonly but mistakenly used ‘tasmanica‘.

Botanists also have had difficulty determining the affinities of this enigmatic little shrub. They variously thought it to be related to the Horizontal bush (Anodopetalum biglandulosum), the Native Laurel (Anopterus glandulosus), and even Saxifrages. Only recently have molecular methods demonstrated that the closest relatives of Tetracarpaea are actually raspworts (Gonocarpus spp. and Haloragis spp.) and watermilfoils (Myriophyllum spp.). Still, the unique traits of the Delicate Laurel dictate that it is best placed in a family of it’s own, the Tetracarpaeaceae.

So there we have it. A true botanical orphan found ONLY in Tasmania.

The ONLY species in the genus.

The ONLY genus in the plant family Tetracarpaeaceae.

A prime example of Tasmania’s botanical heritage.

Forget about beeches, waratahs, pandanis and blue gums for a moment. These long revered icons have been discussed, photographed, drawn and stylized in Australian art ad nauseum. A true connoisseur of plants visiting Tasmania for the first time must embark on a montane pilgrimage and pursue first and foremost the one and only Tetracarpaea.

We don’t look one bit alike, but we are family.

That happens to be the story of a rather obscure group of bryophytes and exemplifies how drastically molecular technology is changing how bryophyte taxonomists study and classify this fascinating group of plants.

Whenever I visit dimly lit gullies in wet forest I always try to look out for bryophytes, one of which is a rather nondescript moss that used to be known as Echinodium hispidum. It was the only one of it’s genus in Tasmania and the nearby New Zealand has another species, E. umbrosum.

A very limpid way of describing this moss without getting into a tirade of alien sounding botanical terms would be to say that it is branched, has spirally arranged leaves that are widened toward the base. A look under the microscope will reveal the nature of the leaves.

Strangely, it is probably the combination of it being rather nondescript and it’s preference for dimly-lit gullies that enables almost instantly recognition of the species for the trained eye.

The genus Echinodium was erected in 1866 and was honored a family status of it’s own, the Echinodiaceae in 1909. Within bryological circles however, the family and genus is of some interest because of it’s anomalous distribution of it’s members: out of 6 species, two are found in Australasia (Australia and New Zealand) and four in Macronesia.

Earlier in 1986, taxonomist Steven Churchill was starting to sense that something was quite amiss with the species of Echinodium. He included all 6 species under Echinodium but was prudent enough to suggest the genus could potentially contain species that are not related to each other.

However, observant as Churchill was with the light microscope, the ‘molecular microscope’ was about to throw a spanner into the works.

In a recent study in 2008, Michael Stech and colleges, compared the specific DNA sequences of the six Echinodium species with species of other moss genera and found robust evidence that the six species of Echinodium did not form cohesive group. The Macronesian species largely remained in the Echinodiaceae but the two Australasian species were actually found to be more closely related with a totally different genus of mosses, Thamnobryum, a member of a totally different moss family, the Neckeraceae.

With such definitive prove of the new generic relationships, Stech and colleges renamed Echinodium hispidum to Thamnobryum hispidum.

Now, while mosses are simply mosses to some, anyone who would take even just a cursory look at the now T. hispidum and compare it to other species of Thamnobryum will find it hard to reconcile this new relationship.

For instance, the commoner Thamnobryum species in Tasmania, T. pumilum, is somewhat dendroid (shaped-like a tree); the leaves are flattened in a single plane; and the plants tends to produce thin wiry branches in addition to normal ones.

No familial resemblance whatsoever between the two species.

Molecular-based taxonomies of bryophytes have lagged behind that of vascular plants but whatever little that has been done is already revealing some rather surprising and revolutionary information that is eroding the very foundations of established taxonomies of the 20th century.

There is always more than meets the microscope when it comes to studying bryophytes!

Tasdendro goes live!

The study of tree rings or dendrochronology is the scientific method of dating the age of trees based on the patterns of tree rings.

The topic of tree rings is close to my heart, particularly given that it is a major part of my current job scope (I work for the Forest Ecology lab in the School of Plant Science and I study the tree rings of an Australian cypress pine Callitris columellaris).

I am hence very pleased to announce the launching of tasdendro.org, a website with the intention of collating all the known information of Tasmanian dendrochronology. The web site was set up under the auspices of the Forest Ecology lab. In particular, Clay Trauernicht, a postgraduate student of the lab, has played a key role in the setup of the website.

The website is coupled with a newly set up storage facility with the purpose of being a repository for tree core material collected from Tasmania.

Given the current interest in climate change and the topic of carbon storage (see my earlier post on Sam Wood’s study), the setting up of such a facility and the Tasdendro website couldn’t have come at a more opportune time!

The Coral Heath (Epacris gunnii) is a fairly common shrub that may be found in wet heath to highland plateaus. This ornamentally attractive plant has heart-shaped leaves with a pointed tip and in it’s full flowering glory produces in a spike-like fashion, numerous flowers in the leaf axils.

In the Royal Tasmanian Botanical Gardens there are many cultivated plants of the Coral Heath, and in particularly, a double form that produces small Camelia-like flowers.

Even though I had the prior awareness the aberration of genetic mechanism of these double form plants, I was still pretty surprised when I stumbled on this strange phenomena of seeing a branch produce a ‘flower’, consisting of a whorl of petals, and have a new shoot growing out of the whorl of petals.

Just to be sure I even sliced the stem and ‘flower’ longitudinally to make sure and indeed, the new shoot just grew continuously out of the whorl of petals.

It is almost as thought the plant decided to make a flower but got sidetracked at the last minute and continued with vegetative shoot growth.

Makes one think, what exactly are flowers?

Many botanists must have pondered on this question.

Thankfully we have some theories.

Thus we learn in botany that flowers consists of four whorls of floral parts in the following order: sepals, petals, stamens (male parts) and carpels (female parts). All flowers are technically modifications of this scheme. And these whorls, some might be surprised to know, are actually modified leaves.

What might come as an even bigger surprise is that the theory of flowers being modified leaves was actually conceived over two centuries ago in the brilliant mind of Johann Wolfgang Goethe, the famous German poet and philosopher.

Goethe, in 1790, had no way of knowing the action of genes in the onset of flowering but his powers of observation would put many a scientist to shame. His insights were discussed his very aptly titled essay, Metamorphosis of Plants.

The concept of flowers being modified leaves might seem very abstract, particularly given the fact that flowers seem to be so different from leaves.

But therein lies the genius of plants. They transmutate. They morph. They make flowers from ‘leaves’. And here it seems our aberrant Coral Heath, leaves from flowers.

There are rather few genera of native Tasmanian plants that share the same genus as the common economic food plants we see in the market everyday. Some examples might come as a surprise however. For instance, Tasmania has one native plant which is a close relative of the CARROT!

The carrot of commerce is botanically known as Daucus carota spp. sativa. In the wild, the species is often referred to as Wild Carrot or Queen Annes Lace. The carrot belongs to the Celery family (Apiaceae), a large botanical family which also includes many plants which will immediately be familiar to the general public, eg fennel, parsley, parsnip, pennyworts, caraway and even hemlock, the source of the poison that killed the famous Greek philosopher Socrates. While the carrot is probably one of the most well known, the genus Daucus actually consists of some 60 species worldwide.

When I saw Tasmania’s answer to the fleshy and succulent carrot of commerce I was pretty amused. This was a small grassland herb, the Australian Carrot (Daucus glocidiatus), which would easily be overlooked as some inconspicuous weed.

Unlike the Wild Carrot, with numerous flowers in showy umbels, the Australian Carrot has a few inconspicuous whistish-pinkish flowers borne on an irregular umbel.

I try not to pick entire plants if I can help it (pretty wimpy for a botanist I know) but I couldn’t help it when it came to this little herb. I just had to check out it’s subterranean parts to see if there was anything carrot-like about this curious little herb.

Turns out that the Australian Carrot does have a taproot but nothing that a bunny would pause at to consider. The affinity of the Australian Carrot to the carrot of commerce had to lie somewhere else.

In the field this little herb is rather easy to identify. Few other native grassland herbs have such finely dissected pinnate leaves. In particular, the small bristly fruits make it instantly recognizable.

And indeed, it is probably the fruits that betray the affinity of the Australian Carrot to the carrot of commerce. In both species the fruits are bristly. In the Australian Carrot, the bristles on the fruits are barbed, as alluded to by the specific epithet ‘glochidiatus‘, which means barbed fruit.

In European herbal lore, the seeds of the Wild Carrot is known to have contraceptive properties (see webpage). If we were to make some extrapolations and speculate, could not the seeds of the Australian Carrot also be used for similar purposes? There certainly is the potential for such medicinal research on native plants.

Classical texts tell us that the Mountain Ash (Eucalyptus regnans), one of the world’s largest flowering plants can attain an age of perhaps 350-450 years. Using dendrochronological methods and radiocarbon dating, Sam Wood from the Forest Ecology Lab has found evidence that these giants attain an age of 500 years.

Prof. David Bowman also appears in the news clip discussing the role of fire in the regeneration of the giants.

And the trees that Sam examined were probably not the oldest!