Hydatellaceae: The Other Basal Angiosperms

Photo by Kevin Thiele licensed under CC BY 2.0

Though rather obscure to most of the world, the genus Trithuria has enjoyed somewhat of a celebrity status in recent years. A paper published in 2007 lifted this tiny group of minuscule aquatic plants out of their spot in Poales and granted them a place among the basal angiosperm lineage Nymphaeales. This was a huge move for such little plants. 

The genus Trithuria contains 12 species, the majority of which reside in Australia, however, two species, T. inconspicua and T. konkanensis, are native to New Zealand and India. They are all aquatic herbs and their diminutive size and inconspicuous appearance make them easy to miss. For quite some time these odd plants were considered to be a group of highly reduced monocots. Their original placement was in the family Centrolepidaceae. All of that changed in 2007.

Close inspection of Trithuria DNA told a much different story. These were not highly reduced monocots after all. Instead, multiple analyses revealed that Trithuria were actually members of the basal angiosperm lineage Nymphaeales. Together with the water lilies (Nymphaeaceae) and the fanworts (Cabombaceae), these plants are living representatives of some of the early days in flowering plant evolution. 

Of course, DNA analysis cannot stand on its own. The results of the new phylogeny had to be corroborated with anatomical evidence. Indeed, closer inspection of the anatomy of Trithuria revealed that these plants are truly distinct from members of Poales based on a series of features including furrowed pollen grains, inverted ovules, and abundant starchy seed storage tissues. Taken together, all of these lines of evidence warranted the construction of a new family - Hydatellaceae.

The 12 species of Trithuria are rather similar in their habits. Many live a largely submerged aquatic lifestyle in shallow estuarine habitats. As you may have guessed, individual plants look like tiny grass-like rosettes. Their small flower size has lent to some of their taxonomic confusion over the years. What was once thought of as individual flowers were revealed to be clusters or heads of highly reduced individual flowers. 

Reproduction for these plants seems like a tricky affair. Some have speculated that water plays a role but close inspections of at least one species revealed that very little pollen transfer takes place in this way. Wind is probably the most common way in which pollen from one plant finds its way to another, however, the reduced size of these flowers and their annual nature means there isn't much time and pollen to go around. It is likely that most of the 12 species of Trithuria are self-pollinated. This is probably quite useful considering the unpredictable nature of their aquatic habitats. It doesn't take much for these tiny aquatic herbs to establish new populations. In total, Trithuria stands as living proof that big things often come in small packages. 

Photo Credits: [1]

Further Reading: [1] [2] [3]

Mighty Magnolias

Magnolias are one of those trees that even the non-botanically minded among us will easily recognize. They are one of the more popular plant groups grown as ornamentals and their symbolism throughout human history is quite interesting. But, for all this attention, few may realize how special magnolias really are. Did you know they they are one of the most ancient flowering plant lineages in existence?

Magnolias first came on to the scene somewhere around 95 million years ago. Although they are not representative of what the earliest flowering plants may have looked like, they do offer us some interesting insights into the evolution of flowers. To start with, the flower bud is enclosed in bracts (modified leaves) instead of more differentiated sepals. The "petals" themselves are not actually petals but tepals, which are also undifferentiated. The most striking aspect of magnolia flower morphology is in the actual reproductive structures themselves.

Magnolias evolved before there were bees. Because of this, the basic structure that makes them unique was in place long before bees could work as a selective pressure in pollination. Beetles are the real pollinators of magnolia flowers. The flowers have a hardened carpel to avoid damage by their gnawing mandibles as the feed. The beetles are after the protein-rich pollen. Because the beetles are interesting in pollen and pollen alone, the flowers mature in a way that ensures cross pollination. The male parts mature first and offer said pollen. The female parts of the flower are second to mature. They produce no reward for the beetles but are instead believed to mimic the male parts, ensuring that the beetles will spend some time exploring and thus effectively pollinating the flowers.

It is pretty neat to think that you don't necessarily have to track down a dawn redwood or a gingko to see a plant that has survived major extinction events. You can find magnolias very close to home with a keen eye. Looking at one, knowing that this is a piece of biology that has worked for millennia, is quite astounding in my opinion.

Further Reading: [1] [2] [3] [4]

Anise: An Angiosperm Success Story

Illicium floridanum Photo by Scott Zona licensed under CC BY-NC 2.0

I must admit there are few flavors I loath more than anise (and consequently licorice and fennel). Regardless of the flavor, I nonetheless find myself enamored by their whorled seed capsules of star anise. In an attempt to reconcile my feelings towards anise in a culinary sense, I decided to get to know the plants that are responsible for it and I am so glad that I did. As it turns out, this group of small trees and shrubs offer us a glimpse at some of the earliest branchings on the angiosperm family tree.

We get star anise from the genus Illicium. Native to humid tropical understories, there are roughly 40 species scattered around southeast Asia, southeastern North America, the Caribbean, and parts of Mexico. Molecular as well as fossil evidence suggests this group diverged during the mid to late Cretaceous, not long after flowering plants came onto the scene. Indeed, along with Amborella and Nymphaeales, Illicium represent the three lineages that are sister to all other flowering plants alive today.

Illicium henryi Photo by Scott Zona licensed under CC BY-NC 2.0

To call them primitive, however, would be a serious misnomer. Because they diverged so early on, these lineages represent serious success stories in flowering plant evolution. Instead, think of them as fruitful early experiments in angiosperm evolution. Illicium has characteristics that set it out as being sister to all other flowering plants. For instance, the vascular tissues more closely resemble those of gymnosperms than they do angiosperms. Also, like the other sister angiosperms, Illicium blur the line between the long standing categories of monocot and eudicot. As such, they are sometimes referred to as "paleoherbs." Another key diagnostic feature lies in their floral morphology.

They don't have what could be considered true petals or sepals. Instead, they have whorls of tepals, which start off sepal-like and gradually become more petal-like as you near the center of the flower. The stamens, which are laminar or leaf-like, are also arranged in a dense whorl surrounding a yet another whorl of fused carpels. Once fertilized, each carpel gives rise to a hard, glossy seed. As the carpels mature and begin to dry, the individual capsules get tighter and tighter until at some point the seed is pinched so hard that it is ejected from a slit in the fruit in projectile fashion.

Illicium verum. Photo by Tim Waters licensed under CC BY-NC-ND 2.0

Although this research will never rectify the taste of this spice, it nonetheless has given me a new found respect and sense of awe for this genus. To look upon the fruit of Illicium is to look at a biological structure that has stood the test of time. These plants are evolutionary successes that should be admired for their unique place in the story of flowering plant evolution.

Photo Credits: Scott Zona and Tim Waters

Further Reading: [1]