Eucalypt flowers and the land of wildfires

One of the best things about my job is going to the field and last week this was made possible, my mission was to visit a eucalypt orchard and collect capsules of Eucalyptus globulus. Perfect! Since I had to collect capsules from the canopy, and eucalypt trees are quite tall, the orchard manager and me had to go in a crane to reach the top of the trees, I couldn’t believe it! It was fantastic and it truly made my day. Even though I have been in even taller canopies before, of different species, in different places and situations, it was for me as marvelous as the first time. It is always fascinating to reach a tree perspective from its canopy – sorry for not having pictures of the moment, but I had to share this with you anyway.

As I was there for capsule collection, I obviously took the chance of collecting some flowers too. I have been looking for eucalypt flowers for quite a while, but the canopies are tall, so I never managed to reach them (I don’t always find a crane next to the trees for a little canopy ride). Eucalypt flowers might not be extremely spectacular in terms of pollination, but their morphology is very interesting – and you have to agree it’s hard to stop looking at these beauties.

Eucalypt flowers diversity: 1 – Eucalyptus rhodantha; 2 – E. kingsmillii; 3 – E. synandra. 
(Photos: https://www.flickr.com/photos/tgerus/)

Since eucalypts belong to Myrtaceae, you do not expect a perianth here, stamens perform the attractive parts of the flower, and the colour attributed to the flower is actually the color of the stamens’ filaments. But even if you are not expecting to find a perianth, it doesn’t mean they don’t have one, or had… Eucalyptus’ perianth is replaced by a protective woody structure – the operculum, which falls at anthesis.

The operculum is maybe the most emblematic structure of the flowers of this genus, but it is not a new structure, it is a modified one instead. The origin of the operculum is actually on the fusion of perianth members (calyx and corolla), but in most groups (e.g. Symphyomyrtus subgenus) you will find two opercula in one flower bud: an outer operculum (of sepal origin) and an inner operculum (of petal origin). In these species, the sepal-derived operculum falls during bud development and the petal-derived one falls at anthesis. So, perianth exists, but is only there on early stages, before anthesis, leaving only a scar on the flower as a reminder of their existence.  

E. globulus flowers; The presence of a scar in the flower bud is a clear evidence that the outer operculum has fallen. Species with a single operculum, or fused opercula, lack this scar. (Photo: Bill Higham)

Another character of Myrtaceae, which has been discussed in another post is the hypanthium. The hypanthium is present in a number of groups, its morphology is labile, as well as the tissues involved, so do not expect to find identical hypanthia in different groups. Eucalypt hypanthia embed the inferior ovaries, and only the style is visible, between the stamina ring and base of the style.

E. globulus buds and flowers at early and later stages.
(Photos: Forest and Kim Starr)

In a later stage, this receptacular structure is involved in the formation of the capsule. Since hypanthium and ovary are structures intimately linked, maturation of the ovary takes place inside the hypanthium and a woody dehiscence capsule is formed. This is why eucalypt capsules are known to be false fruits, because the hypanthium is involved in the process and in the fruit structure. Finally, dehiscence takes place after capsules dry out (usually as a response to dead tissues caused by fire), and capsule opens through valves formed by the splitting of the ovary roof, corresponding to the locules.

When capsules dry out, the ovary roof splits in several valves and seeds are shed through these valves. The number of valves correspond to the number of ovary locules. Scars and rings, corresponding to floral organs, are also still visible in mature capsules. (Photo: John Tann)

Considering the dehiscence behavior and the ecology of eucalypts, I wonder if the formation of these false fruits are actually adaptations to fire. It has been already showed that eucalypt seeds are not fire-resistant, so seed viability relies on the insulating properties of the woody capsules. Perhaps two layers of tissue, the hypanthium combined with the ovary wall, provide higher insulating capacity?

Demystifying Osyris

Whenever we have problems we seek for an answer, an alternative, a way to find a solution. It is not different in the natural world - in fact evolution, the development of new forms and the creation of more diversity has always been triggered by the seeking for survival, outlining problems keeping a place within the ecosystem. During this constant seek, many plants cannot find their place, happening to die and get extinct, some others evolve exploring the resources available.

Parasitic plants are an example that there are no rules for survival in the wild, and obstacles are sometimes to be solved with extreme solutions. Parasitizing others is not the fairest solution, after all the resources used here are robbed and were meant to be used by their hosts, but it was the way these plants found to avoid death and keep on spreading their genes.

There is no particular reason, but I want to talk about Osyris (Santalaceae) this time, simply because I want to share it with you all. It is not an extravagant plant, and neither are their flowers, it is way discrete essentially because it is a hemi-parasitic plant, meaning they are green too as they do photosynthesize. When I learnt the name of this genus, I thought: “Hum, must be related with Osiris, the Egyptian God of the Death, maybe because it is a parasitic plant, and “sucks” the life of other plants”. Well, it could be a good theory in fact, but it was only another contribute from my imagination. The name Osyris is derived from the Greek ozos, meaning branched, relating to the habit of the plant, instead of what I was considering to be the horrific slayer peculiarities of Osyris.

Osiris, the Egyptian God of the Dead was originally a God of Nature, symbolizing the cycle of vegetation

It is hard to describe a typical flower of Osyris, you can find either unisexual (when sex is separated in different flowers) or bisexual, but it is not uncommon in Osyris to find remains of the opposite sex in the flowers. Even though the flowers are very tiny and not showy at all, they have their strategies to seduce pollinators to visit their flowers. Actually, male flowers might have too many distractions; they offer everything to their visitors! The pollinator who decides to come can drink the nectar and taste pollen and staminal hairs.

Male flowers of Osyris alba.
The male flowers of Osyris are grouped in cymes. Please note that these flowers don't have calyx! (Photos: Gianluca Nicolella; Sarah Gregg)

A true feast, and the feast offered by the male flowers contrasts with the stingy female flowers. They have nothing to offer, except three modified yellow anthers (of course without viable pollen), providing only the visual stimulus for the pollinator. So it seems that the female flowers lead pollinators to deception by mimicking male flowers with those “fake” anthers.

Female flower of Osyris alba.
Contrasting with the male flower, the female flower of Osyris are solitary, surrounded by protective bracts. Please note that these flowers don't have calyx! (Photo: Salvador Tello; http://www.flickr.com/photos/salvador_tello/)

But of course there is a reason for everything, and it is not only for being niggard that the female flowers don’t offer proper meals to their tireless pollinators. It is all part of the strategy, this way the pollinators are encouraged to visit all the flowers, some don’t have anything to offer, but they have to go there and check what is there available to drink and eat. Others have a lot of sweets, and this stimulates the little visitors to keep on searching for more from flower to flower, spreading the pollen. It sounds like a good strategy!

In Flanders' Fields the Poppies Blow

Poppies have always give me good childhood memories of fields in late spring, playing with dolls made of poppy flowers is also part of those days spent in the field. Even my mother used to call me “Mary Poppy” when I was a child making of poppies definitely very much familiar and dear flowers to me.

My grandfather taught me how to make poppy dolls like this one...
Source: www.wildplantforager.com

They are, however, associated with heavier and darker topics, such as death and sleep since ancient times and by different cultures, but also more recently with war and the victims of World War I, due to the famous poem “In Flanders Fields”, by John McCrae. Red poppies, Papaver rhoeas, are therefore symbol of wartime remembrance, and are still used in some countries to commemorate those who died in WWI.

 

In Flanders Fields by Willy Werner

But it doesn’t end here, poppy fields have another negative connotation, aside the Flanders fields – and I’m not talking about Papaver rhoeas anymore. I’m talking about Papaver somniferum, also known as the opium poppy. Since ancient times (and by ancient times I mean the Neolithic age!) poppies have been cultivated and used for food, medical and recreational purposes due to its pain relief properties. Oh yes, ancient people from Mesopotamia to Egypt, from India to Persia, they already used this powerful drug. It allowed advances in medicine, with especial emphasis to surgeries, due to the morphine found in the flowers, a powerful anesthetic compound. So, because of its properties, these flowers became associated with sleep, death, drugs and war. Not the greatest subjects to be associated with.

Afghan farmers collecting raw opium in a poppy field
Photo: Rahmat Gul

I’m not going to talk about crops of poppies in Afghanistan and in the Golden Triangle for opium production– enough of such topic! I would like to give you a botanical perspective of this flower too. Papaveraceae – the poppies’ family; is belongs to basal eudicots (order Ranunculales) and are known for having dimerous and dissymmetric flowers, even though exceptions are found in the family, it is quite a stable character. However, Papaveraceae is a somewhat diverse family with 44 genera and 760 species, divided in 2 subfamilies, so I will focus for today on the genus Papaver only.

As you have probably noticed, they do have 4 petals, but if you look carefully you will see that they are inserted in two different whorls – two whorls of two petals. In fact, the calyx is also made out of two sepals, however they tend to be deciduous (falling off after blooming), so it is of no surprise if you don’t find the sepals in a poppy flower. The dissymmetric nature of these flowers is also reflected in other organs, the stamens, the carpels and even the ovules arise in two rows.

But the most interesting structure of the genus Papaver is the gynoecium. The stigmas are laterally confluent, and since they usually don’t have styles (meaning the stigmas are sessile), a stigmatic disc is formed on the top of the ovary – the pollen receptive surface. When ripe, the unilocular but multicarpelate ovary forms a dried fruit, a capsule, together with the stigmatic disc. As a dehiscent fruit, the capsule has valves or pores to allow the seeds to be released from the capsule when dried and ripe.

Left: Morphology of the flower, Papaver rhoeas (Photo: Dennis Heidrich)
Right: Capsule of Papaver somniferum (Photo: http://www.flickr.com/photos/f4/)

Papaver is also a genus know to be bud-pollinated – this means that sexual organs may be ripe before blooming and that pollination may occur even before the flower is open to pollinators! This means that even though poppies cannot control their sexual impulses before flower blooming allowing self-pollination to occur, they found a strategy – they are not self-fertilized due to other mechanisms, a mechanism that even though does not work 100% it can help to avoid selfing! So this means that the fact that self-pollination may occur before blooming doesn’t mean that this flowers don’t need the little flying helpers for cross-pollination, this is why they keep their attractive attributes!

Original, traditional and truly American

Native from North America, the Saguaro cactus can only be found in the Sonoran Desert (US states of Arizona and California and Northwestern Mexico). The peculiarity of such plant is part of the imaginary of the native tribes since ancient times. Many legends have been build-up around the cactus; many of those legends confer special gifts or divine powers to these plants. Its shape and size (which can grow over 20 meters tall) makes a superb view along the desert landscapes, and this was probably the reason why natives believe that the Saguaro cacti were reincarnations of the spirits of Native American warriors, standing in the desert as guardians of their people with arms upwards, supplicating for water and light to the Creator.

Seri People in Sonora Desert, Mexico (Photo: Graciela Iturbide, 1979)

As in a desert whatever you find is a gift from heavens, the Saguaro has been venerated for generations and used as a source of food and shelter for the natives, especially by the Tohono O’odham and the Mexican Seri people, as well as for other inhabitants of the desert. The fruits are an important food source not only for the people but also for birds, whereas the plant itself is used by some species for nesting. The needles were used for sewing, and other parts of the plant were used to build shelters or to produce tools.

A - Parabuteo unicinctus (Photo: Walter Meayers Edwards); B - Micrathene whitneyi (Photo: Bruce D. Taubert); C - Zenaida asiatica; D - Bubo virginianus (Photo: Jim Zipp)

But the real magic happens during the quiet night, when pollination takes place. Any guess on who’s starring this time? Bats! Just take a look at the flowers – white, open, big and on the top of that, it releases a sweet smell of nectar during the night. 

Bat pollination of Saguaro flowers by Leptonycteris yerbabuenae
(Photos by: Merlin Tuttle / Bat Conservation International)  

However during the day the cacti flowers keep opened, so other animals can pollinate when bats are asleep – after all, nothing forbids them to do the job, even though the main pollinator is the lesser long-nosed bat (Leptonycteris yerbabuenae). Unfortunately these bats are threatened and considered Vulnerable according to IUCN, especially due to habitat destruction.

Day pollinators

We have to admit cacti flowers are absolutely gorgeous. More than the natural gorgeousness, they are a botanically interesting case to study. Caryophyllales’ members tend to be odd and have their own peculiarities, and so does Cactaceae, having an immense (botanically speaking, we actually say infinite) number of petaloid tepals. No, not petals – they are not real petals, Caryophyllales lack petals and this is probably one of the reasons why so many different trends arose in this group. They had to find a way to attract pollinators even though they did not have petals to do it! What a task… But they went over it and they reinvented petals with the genetic sources they had. Phenotypically, my dear Cactaceae, I must admit I love what you invented – isn’t Nature truly an artist?

Photo source: Flickr (J Rindrr)