Beyond Fern Fronds

Fig. 1   Fern fronds

A fern that has a flower is not a true fern and anything that resembles a flower on a fern is not a true flower. Ferns are not flowering plants but they are capable of reproduction through spores. The purpose of this article is to point out where this flowerless-reproduction takes place.

New fronds on ferns start out plain green (Fig. 1).  While some fronds are sterile, some are fertile for reproduction which can be differentiated by inspecting the under-side of the fronds as they begin to develop sori - the reproductive structure in ferns (Fig. 2).   

The sori  start out as rows of two dimentional dots (Fig. 2) and as they mature they turn increasingly three-dimensional resulting in an embossed appearance on the fronds. At this point, the sori are enclosed in a thin flap of tissue called indusium.  

Fig. 2.  Sori (singular: sorus) on the underside of  fertile fern fronds.

The indusium at first covers, the entire sorus (Fig.2).  However, as the sori mature, the indusia slowly recede to unveil the growing sporangia (Fig. 3) - each sorus containing clusters of sporangia. Eventually, the and finally detaches from the sorus leaving a velvety house of spores (Fig.4). 

Fig. 3   Indusium slowly revealing the sporangia as they mature.

Sporangium  (Fig. 4) is a receptacle in which asexual spores are developed.  Ferns are flowerless and seedless plants - therefore, they do not undergo sexual fertilization where a male cell unites with a female cell to form a new embryo.  Instead, they have sporangia that are like tiny packages containing multitudes of spores - all potentially capable of cell division to produce a multi-cellular organism - a new plant.  Minute as they are, spores are designed to survive and dispersed - they remain viable for a long time until favorable conditions are met.

Fig. 4    Sporangia all ready for dispersal.

Now that we know about fertile fern fronds that give rise to aggregates of sori that hold the sporangia which are the vessels that contain the spores, we can say that the fronds are not ordinary leaves.  Unlike the leaves of flowering plants which function mainly as sites for photosynthesis, the fern fronds perform dual functions - photosynthetic and reproductive. 

HortiCOOlture - The Mutant Cactus

Fig. 1   Hibotan:  Gymnocalycium mihanovichii var.friedrichii 

Mutation happens when there is a sudden change in the DNA sequence of a gene which contributes largely to the diversity among plants.

Hibotan or Moon Cactus (Gymnocalycium mihanovichii var. friedrichii) is a mutant cactus. This mutation is characterized by the absence of chlorophyll in the plant.  The colors of the normal Gymnocalycium range from green to greenish purple, but their mutated counterparts - lacking the green pigmentation - exhibit bright colors in yellow, pink, creamy-white, orange, or red. 

Plants are by nature autotrophs - capable of producing their own food through the process of photosynthesis. However, the absence of chlorophyll, a key component to photosynthesis, disqualifies the mutant cactus (Hibotan) from being a self-feeding organism.  On their own, they will not survive for more than a week since they cannot produce sugars for nourishment.  However, in spite of its inability to photosynthesize, the absence of the green pigmentation resulted in clear vivid coloration of the plant that mimics the vibrant hue of flowers.  Indeed, the colorful part of the Hibotan (Fig. 1) is not a flower.  On the contrary, it is a handicapped plant that is grafted to a physiologically functioning plant for nutritional support.  The composite plant with brightly colored scion on green stock creates an appearance of a cactus in bloom (Fig.1).

It is not a flower -- it is a chlorophyll-free cactus attached to a green stock.

HortiCOOLture - Armored Plant

Fig. 1   The bizarre porcupine tomato (Solanum pyracanthum).



Ornamentally Odd
When all the basic plants are in place in the garden, an oddity here and there is in order.  This week our local nursery is offering a plant that would fit the bill.  The "Porcupine tomato" botanically known as Solanum pyracanthum (Fig. 1) is a plant that is armored with spikes all over. 

In spite of being prickly, some ornamental features can be attributed to this plant.  The bright orange spikes provide a pleasing textural and color contrast against the bluish green velvety leaves (Fig. 2).  The royal purple petals are complemented by protruding yellow stamens in the middle.   Eventually, small cherry-tomato-like fruits will take the place of the colorful flowers. A plant with such attributes definitely makes a statement in any garden.

Fig. 2   Dagger-like spikes on land under leaves of Solanum pyracanthum

Physical and Chemical Threat
This may be an ornamental shrub but the plant is definitely for your eyes only. The velvety green leaves may look soft and friendly but the dagger-like spikes (Fig. 2) that are spread all over the plant  make the plant look utterly foreboding.   I would not recommend this plant near playground areas.  The quills would deter any one from touching the plant but the danger does not end there.  The plant is known to contain various toxic substances on the leaves, stems and fruits - just like most solanaceous (night shade) plants.   Because of this, it is not clear whether the spikes were meant to protect the plant from humans and animals or vice versa. 

Fig. 3  Solanum pyrachantum flower.

 

 Fig. 4   Armored fruit of Solanum pyrachantum. (Photo from Rob's Plants)

 

 

Threat of Invasion

The plant is drought tolerant therefore caution should be observed when it comes to cultivating this plant since it can be invasive depending on the growing conditions.  The fruits are loaded with seeds which when allowed to mature and fall on the ground will result in an explosion of new seedlings.  Eradicating an army of plants like this, would involve a bloody battle.  :)  

 Solanum pyrachantum, although related to food crops like potato, tomato and eggplant, has been cultivated solely as ornamental plant.  And we will keep it that way! 

HortiCOOLture: Enormous Aloe

Fig. 1   Aloe arborescens  (February 18, 2012 Pacific Grove, California)

A. arborescens, also known as A. perfoliata var. arborescens is commonly named as Octopus plant, Candelabra aloe, or Torch plant.  The plant is multi-branched with rosettes of tentacle-like, partly concave leaves, thus the name octopus.  Like most succulents, A. arborescens blooms once a year (spring to summer).  Each rosette then sends out a terminal upright raceme that is covered with red flowers - transforming the plant to resemble the appearance of a chandelier (Fig. 1). 

According to the AHS, this plant is a native of Malawi, Mozambique, Zimbabwe, and South Africa.  Based on the size of this plant (Fig. 1), however, the California coast seems to provide favorable conditions for its growth.  

This enormous Aloe arborescens is stunning but I will not have it in my yard because its leaves are sharply-serrated. 

HortiCOOLture - Spiderweb-like Hair

The Sempervivum arachnoideum is very unique succulent in that it has the appearance of an organized entanglement. If you are not familiar with this plant you might get the impression that they are infested with spiders.  On the contrary, those webby structures on the leaves could be a defense mechanism against insects. 

Trichomes loosely connect leaves together.

The white webs on the leaves are specialized trichomes that connect the leaves together.  As seen from the picture above, there are normal trichomes (hairs) on the surface of the leaves but those that form the webs are coming mainly from the pointy tip and margins of the leaves.  These spiderweb-like trichomes stretch as the leaves grow.  That is why they are increasingly longer and sparse on the periphery of the rosette.  The growth of the trichomes starts with the growth of the leaves as indicated by the concentration of very tight webs in the middle. 

Trichomes are "leaf hairs".    They come in different forms and in some cases there are different types of trichomes in one leaf as exemplified by the Sempervivum arachnoideum.  (Just like in humans and animals - the hair that grows on the head is different from those that grow on the arms, so is in plants.) They have different functions depending on the nature or habitat of the plants.  Trichomes can serve as a deterrent to insects.  Also they can serve as defensive layer against extreme environmental conditions such as wind, heat, cold, ultraviolet rays.  In some cases trichomes also serve as a mechanism for salt tolerance. 

Webby trichomes make the plants look frosty.

Sempervivum arachnoideum is a type of succulent that originated from the Alps (1) and I believe that their trichomes play an important role in its ability to adapt in the snowy, windy and cold conditions of the Alpine Mountains.  It is an evergreen plant and can tolerate freezing temperatures.  Although they do well in dry conditions, adequate water helps the tiny plants to grow at a faster rate. 

Pink flowers float from the multitudes of Sempervivum aracnoideum rosettes.

Sempervivum arachnoideum is a plant to give to an arachnophobe. :)

Happy Halloween!

1) Elijah Walton, Thomas George Bonney (1869).  Flowers from the Upper Alps: With Glimpses of Their Homes

HortiCOOLture - Downward Growth

Senecio spp.  'Oribi Gorge' 

It has been my observation that the 'Oribi Gorge', a succulent plant, has a very unique behavior when it blooms.  The stems that bear the flower bend downward.   It is very interesting.

Natural position of the flowers in relation to the plant itself.

Propped up flower to highlight details. 

 

Architecturally pleasing.

Bright orange flowers inside powdery green sepals.

Flower at maximum aperture.

This is a relatively new plant in my garden which continues to be a subject of my fascination.

HortiCOOLture - Bolting Power

Agave applanata

This plant grows very close to the ground until it starts to bolt.  Then it sends out its flower up high for everyone to see.   This picture was taken at the UC Davis Arboretum a week ago.

HortiCOOLture - Uncommon Beauty

Senecio spp.  'Oribi Gorge'

This is the flower of a succulent plant from the Senecio species.   Other plants under this family look different from this plant.  There are several plants classified under the group and the only possible resemblance of the 'Oribi Gorge' with other plants that I see would be the characteristics of their flowers.

Senecio is derived from a Latin word senex meaning old man which could be seen in the fluffy white seed heads of senecio plants plants.  If you look at the picture above, you can see a glimpse of the individual flowers within a flower.  Each of those tiny yellow flowers is capable of being fertilized and becoming seeds called achenes.  For the 'Oribi Gorge' I still have to see what happens.  Right now the flower is opening at a very slow rate measured only in nanometers (nm) per day.  While we wait therefore, I invite you to focus on appreciating the beautiful architecture of its flowers.

 

Senecio spp. 'Oribi Gorge'

The 'Oribi Gorge' was named after the place where it was discovered in South Africa.   Although it is a succulent, it prefers to be watered well during the hotter months to look beautiful.

Clematis Seed Heads

Seed head from Clematis 'Nelly Moser'

After the colorful petals of the Clematis 'Nelly Moser' flowers have all fallen off the seed head is all that's left.  The seed head has a metallic sheen that distinguishes itself from the leaves of the plant.  Some of them look like a ball of yarn or koosh balls.  The tails look spidery because they are hairy.  Other varieties have seed heads that are not as

The seed head is the fruit of the plant.  The stringy parts are seed tails which are attached to the seed pod better known as achene.  When the seeds ripen the tails change from sleek to fluffy.  I could see how this would aid natural seed dispersal as they can be carried by wind just like dandelion (Taraxacum officinale) seeds.  For clematis however, it is advisable to dead head them as it might lengthen their flowering period depending on other factors.

Clematis Seed heads

Happy Sunday!

Framing a View

Have a nice wonderful Sunday afternoon in your garden today!

HortiCOOLture - Flowers Turning Into Fruit

Developing pear fruit.

I was in my garden the other day and saw these tiny fruits.  They look dainty now but soon they can be up to one-pound-size fruits.

The fruit of the pear (Pyrus communis) is considered an accessory fruit.   Accessory fruits are sometimes referred to as false fruits because technically, the fleshy part of the fruit that we eat is not the fruit.  Instead it is the enlarged receptacle.  The fruit is described as the ripened ovary.  In the case of the pear or apple the actual fruit is the core.  If you look at the picture above, remnants of the flower other parts are still visible and yet the receptacle is obviously in the process of enlarging.   The receptacle will continue to enlarge and envelop the developing fruit (core) which contains the seed.  Thanks to the receptacle or else the pear fruit would be of little food value.  To understand this concept better, look at the illustrated parts of a flower.

Stroll in your garden...it's good for you and your plants.

HortiCOOLture - Interesting Tree Bark

Layers of peeling bark on a birch tree

This is an interesting bark display on a birch tree which I see often as I walk to Starbucks on most mornings.   For this tree, the peeling bark coupled with its soft earth-tone coloration is definitely its most distinctive feature.   I wonder what variety of birch tree this is.

HortiCOOLture - Japanese Maple

Acer plamatum 'Bloodgood'

Starting today I plan to post a 'HortiCOOLture' picture every Sunday.  This would be something that speaks of the wonders of plant life and their environment.  To begin with, I have this  Japanese Maple leaves and samaras taken after the rain. 

Samaras are a type of fruit where in the seed is enclosed by a thin tissue that extends out forming a wing-like structure. The wing-like structure eventually facilitates the natural transport or dispersal of the seeds. 

 
That is very cool!