Ranunculaceae and the origin of petals

There are events that change the course of evolution. In my opinion one of the most important events that have changed the course of evolution in flowering plants was the transition between spiral to cyclic flowers. This episode was obviously gradual as everything in Nature is, but it is still incredible to observe this transition in living plants and there is a group telling us this episode better then any other.

Early diverging eudicots from APG III tree

Early diverging eudicots is the transitional group between basal angiosperms and core eudicots. In fact, plants belonging to this group are inbetweeners, they share characters from both groups, bringing an extreme floral diversity to the plant world. They were the authors of many innovations, such as nectaries, zygomorphy, perianth differentiation in two different whorls (calyx and corolla) and many other novelties. One of the best examples of this diversity is Ranunculaceae, and today I have brought one of the most stunning creations of this family in the form of Aquilegia. In fact, most members of Ranunculaceae have incredible structures where you can almost interpret the gradual formation of cyclic flowers, many of them with extravagant nectaries acting also as petals. Aquilegia is just another example, and the flowers are pretty much incredible!

Side view (left) and front view (right) of Aquilegia flower

In Aquilegia, pentamery is already established, and we can easily find the bipartite perianth with 5 sepals and 5 petals. The petals, however have a very particular character – they are spurred, producing nectar to attract pollinators. This is the reason why many authors prefer using the term “nectar leaves” instead of “petals” in Ranunculaceae.

Left: View of the back of Aquilegia flower; Right: Detail of Nectar leaf of Aquilegia

These nectar leaves are of extreme importance on the evolution of a bipartite perianth, and in Ranunculaceae this transitional situation is still visible. They are not true petals yet, but structurally that’s how we interpret these structures. The tepals, structurally acting as sepals in this Aquilegia are the true perianth members of the flower. The nectar leaves are nothing more than stamens that lost their original reproductive function, becoming staminodes (or sterile stamens) and latter gaining a new function to attract pollinators. This is how true petals were born, they are nothing but modified staminodes that evolved in the direction of pollinator attraction. On the other hand, sepals evolved directly from tepals (leaves) gaining the function of organ protection (the reproductive organs – stamens and carpels).

Origin of petals in Aquilegia. The outer whorl of stamens loosing the reproductive function, and gaining later the function of pollinator attraction, becoming showy  and colourful (like petals) and producing nectar. Tepals at the same time gain the function of flower protection, like sepals.

However, some researchers believe that the origin of petals is not entirely the same for all members of Ranunculaceae. Some members of the family might indeed have their bipartite perianth as a result of the ascension of the bracts to the base of the receptacle, originating the sepals. Likewise, the true perianth (the tepals) gave origin to the petals. Ranunculaceae seems to be a family of flower structure experiments, trying which structure is the best to have. In any case, it seems that after this group pentamery and bipartite perianth were successfully achieved characters, well established in the rest of Eudicots.

The Portuguese Oak

I have decided to honor Portugal with this week’s post for two reasons: to celebrate the National Day of Portugal (which was last Sunday , the 10^th of June), but also to support the Portuguese team at the UEFA Euro 2012. So I have decided to bring you today the Portuguese national plant – Quercus suber, the cork oak.

Quercus is a monoecious anemophilous plant, meaning that the sexual organs are separated in different flowers and are wind-pollinated. Thus the flowers are simple, small and shy, with a rather simple structure, but I thought this is a good opportunity to introduce you the wonders of wind-pollination. Anemophilous plants (wind-pollinated) are mainly found in two orders: Fagales and Poales and this, first of all, give us some clues about the environment shared among wind-pollinated plants. They are either trees (Fagales) or grasses (Poales), possibly due to the fact that flowers bloom high in the canopy, where the pollen is easily reached by the wind, but not as much by small insects. Another reason is possibly the windy and dry conditions found in steppes or desert-like environments where grasses reign. In such environments, the wind is a common and available resource much prevalent and reliable than insects. Possibly, also due to the winds typical of such environments insects are here less abundant comparing with, for example, forest-like environments. For this reason, plants found here have started to invest their energy in other characters, allowing a more efficient pollination and thus the flowers became adapted to wind pollination.

To make it easier for you to understand the main differences between anemophilous and entomophilous (insect-pollinated) plants, I have made this table to share with you:

Comparision between Anemophilous and Entomophilous floral characters

Because anemophilous plants have no need to attract anything, there is no need to invest energy producing big showy flowers, or expensive precious nectar. Instead, these plants produce many small flowers and large quantities of light pollen, which can be easily carried away by the wind. To facilitate the wind to take the pollen away, the petals are much reduced, and sometimes they are completely missing. Likewise, the stamens are hanging outside the flowers, waiting for the breeze.

Male inflorescence of  Quercus suber with the stamens hanging outside the flowers
(Source: www.flora-on.pt)

Also the typical inflorescences found in Fagales are definitely adapted to this pollination syndrome. Catkins of small and light flowers are easily moved and shacked even by a light breeze, and this allows the pollen to be released and spread easily. Because the pollination isn’t specialized like in entomophilous plants, the stigmas also have to be adapted to the wind pollination, so the surface of pollen reception is much bigger. This can be very easily observed in Poales, where the stigmas are long and feather-like, increasing the surface for an effective pollen reception.

Feather-like stigmas typical of grasses. Left: Arrhenatherum album; Right: Ammophila arenaria (Source: www.flora-on.pt)

Also, the position of the inflorescences in the tree isn’t random – male flowers are found in the lower older twigs and female flowers in the upper younger twigs. This is to avoid self-pollination (it is more unlikely that the pollen from below flies up and fertilizes the female flowers, but if female flowers were below, any pollen grain falling from the catkins above could fertilize them).

Flowers and inflorescences of Quercus suber

Wind-pollinated flowers are so shy that they can be unnoticed many times, especially by non-botanists. The truth is that they are not hiding, they are right there and it is fascinating to observe all the structures that seem to be undercover by the green foliage. Finding them is like finding a precious treasure, which is visible for everyone, but unnoticed by most people. That is the reason why every time I show wind-pollinated flowers to non-botanists they become astonished and quite surprised... These flowers might not be the prettiest, but they are pretty cool too.

The Passion flower

What is the first think you think of when someone mentions passion? Perhaps romantic love? Physical or sexual attraction for someone, or maybe just sex? Do you think of the same meaning of passion when the subject is the passion vine? What is the origin of this plant’s name? Is the passion fruit an exotic aphrodisiac? Well, not exactly but maybe if you’re in the right mood anything can work as an aphrodisiac...

Passiflora (Passifloraceae), the genus of the passion vine, gained this name due to the great imagination and devotion of the Portuguese and Spanish Jesuits which associated most morphological characters of the plant to symbols of the Passion of Christ. While exploring the exotic tropical rainforests of South-America they were astonished not only by the beauty and diversity of the plant (Northern-Central Brazil is an important hotspot of diversity for these plants) but also with all the symbolism that they immediately attributed to the plant. For the Jesuits, the flower of the passion vine had all the symbols of the Passion of Christ, and so it was named after this passion, not any other romantic or sensual passion that people might probably think of – after all it is indeed an exotic and extremely sweet fruit.

Flower diversity in Passiflora sp.

So now you are curious about the symbols, and the Jesuits were indeed very attentive – they looked at all the flower organs finding explanations for numbers and shapes of most of them. Let’s see…

The flower is pentamerous, with 5 sepals and 5 petals, representing the 10 faithful apostles (excluding Peter, the denier and Judas, the betrayer); the corona represents the crown of thorns with which roman soldiers crowned him as the “King of the Jews”; the ovary, a chalice shaped structure, represents the Holy Grail; the 3 stigmas represent the 3 nails used in Christ’s crucifixion and the 5 anthers the 5 wounds (1 in each hand and foot and the last one in his chest caused by the Holy Lance). But not only the floral structures were considered to be the symbols of the Passion of Christ. The characteristic leaves with pointed tips resemble the Holy Lance that confirmed Christ’s death and the tendrils represent the whips during the flagellation. The colours have also been attributed a meaning, since many species are white and blue colors, representing heaven and purity, and we must not forget the purple, which was also the colour of the robe that romans covered Jesus after crowning him.

The association between the flower and symbols of the Passion of Christ

Apart of all the symbolism involving the plant, there are also interesting characters related with the ecology of the plant that I would like to share with you. Every single part of it is edible, meaning that this plant is the herbivore heaven! They can eat the leaves, tendrils, flowers and there is plenty of nectar in the floral and extra-floral nectaries. To avoid getting eaten by all the herbivores, Passiflora seem to have made a deal with the ants by feeding them with nectar from extra-floral nectaries (usually present in bracts but also in leaves). Likewise, the ants protect their plant from herbivores and nectar robbers. Also the ants allow true pollinators to access the floral nectaries, allowing the successful reproduction of the plant. It sounds beautiful, but it is not as simple as it might sound – it relates many ant species, so a lot of different behaviours with different Passiflora species and environments. In any case, Passiflora and ants seem to get along very well and it seems to be a fair symbiotic relationship.

Ants feeding on nectar from extra-floral nectaries of the bracts of Passiflora

After attributing so many symbols to this plant, I wonder what Jesuits thought noticing so many ants around the vines getting rid of the hungry predators, protecting their “holy” source in exchange of precious nectar. I will let you meditate on this, wishing you a blessed Thursday of Corpus Christi.

Long wait, but with new stories to come!

Dear readers,

I am very happy to announce that I am finally back home, and so are the tales! I have been traveling since my last publication, and I found out later the impossibility of traveling and getting organized with good stories and pictures to publish. But I am back now and there is a lot to share! During these trips I have been to many different environments and seen a lot of beautiful flowers.

Each flower has a story to tell – the story of their past, and I try to translate them to you. But also because plants have a deep presence in human cultures, people have interpreted plants and flowers in different ways, giving them meanings and telling other stories which I found amazing and would be pleased to share with you!

A new story is ready to be published tomorrow – don’t miss it! J

Myrtaceae and the Bombacaceous-Malvaceae

“Someone brought this for you today”, he said smiling. It was a flower and it had a smell of challenge too. It was a big white flower with many long stamens, fused in the base in groups. The style was sticking out from the middle of the stamens tube and it also has a profound cup-shaped hypanthim and 5 long white petals. “Humm, stamens fused at the base with the style like this is a very Malvaceae-like character… But the most obvious character of this flower is definitely the large number of long stamens with only one style coming from the middle”, I thought innocently, “Humm, plus this hypanthium, it looks very Myrtaceous”.

Myrtaceae?! Tremendous fail!

After a while I found out I was looking at a Bombax anceps flower, a common tree here in northern Thailand, belonging to the old Bombacaceae (now Malvaceae – yes, Malvaceae!). The tree is easily identifiable because of the thorns found in the bark, and at this time of the year also because of the big and showy white flowers and no leaves (it is a deciduous tree).

Young Bombax anceps bark and flowers - It actually looks quite Myrtaceous from a distance

These flowers produce an amazing smell due to the large amounts of nectar secreted in the morning, attracting many birds for the pollination daily-service.

Evidence of pollinators having nectar of Bombax ceiba for breakfast

Everyday I see this small beautiful tree, but it only started flowering a few days ago, and let me tell you it is a must-see not only for flower-freaks (like me) but for everyone – every time I pass by the tree with someone else I hear their “Wow’s”… No wonder!

But why was I so confused between these two families, Myrtaceae and Malvaceae? There should be nothing to be confused about; in fact they do belong to their own orders, Myrtales and Malvales, meaning that they are quite different. But they do have similarities also: both Malvales and Myrtales belong to the Rosids (actually to the same branch in the Rosids – the Malvids), and that might explain morphological misunderstandings.

Malvaceae flowers are characterized for having a synandrium, a structure where all the stamens are fused together with the style coming from the middle of the synandrium. Another good character is the contorted corolla fused basally with the androecium. The number of stamens is very much variable, ranging from 5 to many, however when many they are grouped in 5 or 10 groups, depending on the number of whorls (one in Bombax anceps and two in Bombax ceiba).

You can probably summarize a Myrtaceae-like flower with 3 main characters: large hypanthium, a lot of long (showy) stamens and reduced petals. In Myrtaceae the hypanthium is very much developed, having a high number of stamens placed at the top (the ring of stamens). Bombax anceps flowers reminded me of Myrtaceae flowers because I totally ignored one of these characters: the petals! But also the stamens are different – in Myrtaceae they are not fused together, not in groups or in synandria, so why did I think about Myrtaceae when I looked at the flower? Because of the calyx shape in Bombax anceps flower, which resembles a hypanthium.

Find the differences (the B. anceps flower didn’t have style anymore when I took the picture, but it was long and red as you can probably see in the first picture of this post)

The hypanthium is a structure sometimes hard to identify and define, and originating many times misunderstandings on the interpretation of the morphology of the flower. This means that it is an important structure to help us to find the big group (Rosids), but we cannot ignore the other structures. 

The Tết’s flower

Have you been looking at the moon? It’s getting smaller and smaller and smaller…The New Moon is coming very soon, and so is the Lunar New Year! To celebrate this very special date, I will dedicate a post to a very special flower used in the Vietnamese (and maybe in other nations?) traditional celebrations of the Lunar New Year, or “Tết”. The first time I saw these flowers was here in Thailand and they kept my attention because of weirdness of their looks...

What else can I say? It looks just weird to me!

Since the first time I saw this flower I wondered to which family it belongs to, but the morphological clues didn’t ring me any bell - at all! I had no idea about the family of this plant. Until one day, when my Vietnamese herpetologist friend suggested me to talk about one of the most famous plants in Vietnam – Ochna integerrima. I was very much surprised when I realized that it was the flower I was wondering about for so many weeks! Thank you in advance for this, Ha. 

Ochna belongs to its own family, Ochnaceae and no wonder I could not identify this family – I have to admit I knew very little about Ochnaceae until now! But now I can say that I know little enough to dedicate one entire post to these flowers. Ochna integerrima is the most celebrated plant in Vietnam, because it blooms during the Tết, having a special meaning for Vietnamese culture. The Vietnamese believe that these bright yellow flowers bring luck and prosperity for the coming year.

Source: http://www.freephotos.biz

Another curiosity about this plant came up while I was googling “Ochna integerrima”, coming up automatically “Vietnamese Mickey Mouse Plant”… This common name made sense to me as I had seen the plant already, but for those who have never seen or heard about it before it might sound strange. This plant produces some beautiful round-shaped black berries on a bright-red head-like receptacle. So probably, some cartoon-lover botanist saw Mickey Mouse’s ears on the berries and decided to name it this way!

Fair enough!

After what happened I had to search about this family and will give you now some tips so we can all easily identify Ochnaceae. No more excuses! The flowers are usually pentamerous, having 5 sepals (usually enlarging in fructification) and 5 free petals (often caducous). The number of carpels is variable, sometimes fused having a terminal style, or if free with a gynobasic style.

Unfortunately, I didn’t find any flower with the petals as they are caducous and I only found later stages, already forming fruit

So now that we all know how an Ochnaceae flower looks like, I would like to wish you happy celebrations for those who celebrate. For those who do not usually celebrate, I suggest you to spend some time looking at the sky for a change, trying to find the New Moon!

Happy Lunar New Year everyone! =)

Well-behaved plants live in wild Borneo

Probably the most interesting group of plants for the majority of people are the carnivorous plants because of their behaviour with insects. Wait, because of the insects’ behaviour with these plants! Well, in any case we must all agree that carnivorous plants were a wild invention of Nature. 

Different growth stages of pitchers in the QBG carnivorous plants glasshouse

My opinion about them became even wilder when I found an old article about a Bornean pitcher plant (Nepenthes bicalcarata), which relationship with insects is absolutely unexpected for a carnivorous plant. So first, let me remind you some aspects about the biology of these plants: pitcher plants are known by getting nutrients from insects as a supplement. Their strategy is to attract insects using a trap, a modified leaf (the pitcher), which is full of enzymes and digestive liquid where the nutrients can be absorbed. 

In Nepenthaceae, the leaves are differentiated into pitchers and the petioles are the photosynthetic part of the plant, having the function of the leaf but not being a true leaf

The insects are attracted by the extra-floral nectaries and often fell in, drowning in the fluid. However this particular species, Nepenthes bicalcarata, nests ants (Camponotus schmitzi) in their swollen and hollow tendrils. Strangely, these ants forage on the inner side of the pitcher, crawling over the slippery walls without difficulty and even swimming in the pitcher fluid to forage and feed on the insect prey’s of pitchers. So, what is the advantage for the plant on having other insects eating the food that they get alone by using their own pitchers? The ants only collect large prey insects – all the other small insects are digested and absorbed by the plant. Big preys take long time to digest, and this would end up on putrefaction and rotten pitchers, which is obviously something not very healthy for a pitcher plant to have. So these pitcher plants get rid of the large preys by offering them to their friends - ants. “Wow!” – I can hear you guys whisper. No worries, I whispered the same – these plants are really something!

Picture of Nepenthes calcarata sourced from the magical internet. It is possible to see the nests that the plant produces in the tendrils, as well as the "horns" that are very characteristic of this species

Even though this is all undoubtedly very interesting, the flowers of Nepenthes do also tell a story. Nepenthaceae, as all the members of Caryophyllales order have no petals, so their perianth has only one single whorl made out of sepals. The flowers are also easily recognizable by being dioecious (meaning that sexes are separated in different flowers, male and female) and tetramerous. Of course that a carnivorous plant also needs insects for pollination, so they do produce a lot of nectar to attract a lot of insects. Some will end up in the pitcher-insect-hell, but others will end up licking the sepals which are fully loaded with sweet nectar. It’s a matter of luck for insects I suppose.

Typical inflorescence of Nepenthes, a racemose with paired tetramerous flowers, each one subtended by one bract

Another very interesting fact about the Nepenthes are the male flowers, which have all the stamens (ranging usually from 4 to 24 in number) fused together in a structure which botanists decided to call “synandrium” (syn meaning fused and andrium referring to the male part).