Over a period of hundreds of years, a great part of the original forest vegetation of Madagascar’s Central Plateau has been destroyed by annual burning.
The resulting savannah-like grasslands are very poor in species. A few succulents can survive the fires, either because they have very thick and fleshy leaves, e.g. the subject of this post, or because they hide underground (such as geophytic Euphorbias, see Euphorbia primulifolia).
A. macroclada is an impressive plant with its leaves up to a meter long and 17-22 cm wide at the base. In winter, the stemless rosettes are adorned with (usually single) inflorescences which in old specimens may be up to 2.5m tall. The many flowers are 2-2.5 cm long and 2 cm wide at the mouth.
It is probably the most widely distributed of the Madagascan Aloes, from 200 km north of Antananarivo to Fort Dauphin in the far south, usually at altitudes between 1200 and 1500 m.
Because of the peculiar orientation of its leaves, this species is often called Vertical Leaf Senecio or propeller plant.
The plants have creeping to erect stems, to 80 cm tall and much-branched.
The vertically flattened leaves* are variable in shape, size and colour, to 10 cm long, 3 cm wide and 3-5 mm thick.
Inflorescences are to a meter tall.
The species is widespread in central and southern Madagascar, where it grows on denuded granite rocks, often together with members of the Euphorbia milii groep, such as E. horombensis and E. fianarantsoae and Pachypodium species (first picture shows P. horombense in foreground).
* This vertical compression of the leaves is usually regarded as an adaptation which reduces the amount of light that reaches the leaf surface, resulting in lower daily water loss than in leaves in other orientations.
Pictures 3 and 4 show plants in cultivation (scans of old slides)
At the end of our latest trip to Madagascar, we stayed in Antsirabe, south of the capital Antananarivo. The area is well known for its succulents and I decided to spend an afternoon in the mountains surrounding the town. For several kilometers the road leading out of town ran through the middle of a wide valley, and what I could see of the mountain slopes did not look promising at all. At a certain moment we decide to take a little side road that seemed to take us out of the valley. This was indeed the case, but even the hillsides appeared to be cultivated.
When the driver asked talked some local people if there were any bare rocks nearby, he got a positive reply, but in spite of their directions no rocks came into view. At a loss what to do now, I decided to just stop at an uncultivated spot and look around.
Picture #1 shows the first plant that I noticed there. Without flowers it could be about anything, but next to it was a group of flowering plants (#2) and immediately the penny dropped.
With a large tuber 10-15 cm long and to 7 cm thick, Euph. primulifolia is a true geophyte. It has a very short stem, hidden in the ground, with a radial rosette of 4-12 leaves. In the dry season the plants are leafless and hidden in the grass; in other words, they are only visible in the rainy season. This growth form allows the plants to survive the yearly grass burning.
The leaves are flat or undulate, 8-11 cm long and 3-4 cm wide.
Usually the plants flower before the leaves appear, but as the pictures show, this was not the case here. The cyatophylls* vary from white or greenish to pink and violet.
This variable species is widespread in the central highlands at about 1400-1500 m in a variety of substrates.
* cyatophylls are the bracts that surround the inflorescence proper in many members of the Euphorbiaceae.
Plant in cultivation. Scanned slide.
Because this species is often more or less climbing in surrounding shrubs, it is difficult to spot when not in flower. The name refers to the very narrow leaves, which are up to 13 cm long, but not more than 1 cm wide.
The plants become up to 1.5 m tall and produce brilliant red flowers with a tube just over 1 cm long.
One can find the plants in a wide strip roughly following the coast of southern Madagascar from Fort Dauphin to Tulear, where they mainly grow in xerophytic bush on limestone rocks.
The photos were taken at Madagascar’s southernmost tip (Cap Ste Marie) on 2 Nov. 2016.
To see this species in the wild, you have to go to the far north of Madagascar. The plants grow there abundantly on limestone on the Montagne des Français and neighbouring hills near Antsiranana. The old -but still often used- name for this town is Diego Suarez (hence the specific epithet).
The plants are solitary, with or without a short stem, with leaves up to 60 cm long and 10 cm wide.
They produce inflorescences 60-80 cm tall, with 4-12 branches. The flowers have a length of about 2.8 cm and are covered with very short, soft hairs.
As a young plant, this species looks rather uninteresting, but that changes dramatically over time. Unfortunately not many readers will have the time and the space needed to grow a specimen to perfection, but in north and west Madagascar, where it is endemic, it is often grown as an ornamental tree (see first picture). It is also a characteristic component of deciduous forests and palm savannas.
These pachycaul trees may become 3-6 m tall, with a swollen stem-base 50-70 cm in diameter and deciduous leaves 16 cm long and 4.5 cm wide.
The inflorescences appear at the branch tips and bear numerous white flowers with
lobes 2-4 cm long and about 2 cm wide.
For a little prologue to this post, see the preceding one: Kalanchoe integrifolia).
Although Mt. Ibity is perhaps the most accessible place, P. brevicaule also occurs in a couple of other habitats in Madagascars central highlands.
Plants can be found from Ambositra to Antananarivo in quartz rock at altitudes between 1400 and 1600 m.
In some spots where P. brevicaule grows together with P. densiflorum or P. rosulatum, one can come across hybrids. Judging from the long flower stalks, I suppose the plants shown in pictures # 3 and 4 belong to either of these hybrids.
The first two pictures show views from where P. brevicaule grows on Mt. Ibity. On # 2 you can see the quarry belonging to the massive cement factory nearby.