Biology & Cultivation of Aloe polyphylla
Reproduction of this species is nearly impossible via the commontechnique taking stem cuttings because of the acaulescent habit.For all other caulescent species in the genus this is easy to do. Yeteven this method produces only a few plants. Seed germination isjust as difficult because plants rarely flower and the pollinationbiology is set up to produce outcrossing only, with maturation ofanthers and stigmas separated in space and time .Two plants ofdiffering genotype flowering synchronously are needed to producehybrid seed .This is again a great restriction for any growerwishing to produce hundreds of spiral aloes.
Some individuals have developed tissue culture techniqueswhich also have a downside. This photo shows a 5 year old t.c.plant with a confused leaf sequence. In year 8 these plantscorrected themselves ! Real seedling have no such handicap.Tissue culture cannot become the preferred method of reproductionbecause of this factor. The preservation of any endangered species rests on increasing the genetic diversity. Cloning can not satisfy this.
The pollination biology creates hybrid seed almost exclusively. These photos show the developing inflorescence . The first flower to open is on the bottom row, and the anthesis (the sequential opening of single flowers) proceeds to the uppermost flowers. The erect unopened flowers fall pendulous and the anthers are elongated first and then release pollen. The nectaries at the base then release nectar for the Malachite Sunbird’s pollination services. After the anthers have dehisced the style is elongated ,the stigma protrudes beyond the corolla lip and becomes receptive. Each flower may produce 51 seeds from 3 locules of 17 embryos each when pollinated. After pollination the pendulous flower stands upright as the seed matures ! The epidermis of the seed capsule has fully functional chlorophyll.
Developing inflorescence comes from mid spiral, not the center. The upward pointing scales are sepals sheathing each flower.
Exerted stigma not receptive to pollen until the stigma forms to allow pollen tube to grow up towards the ovules.
Exerted anthers opening to release pollen before the style elongates . Stigma receptivity follows to provide for pollen tube growth to ovule.
This photo shows it all : upright seed capsule maturing, pendulous flowers open, and upright unopened flowers at top.
Seed germination is difficult and after 35 years of various trials I still do not have any definitive statements to make, only observations. Scarifying the outer membranous wings shortens the imbibition period , but may also contribute leakage of carbohydrate which enables fungi to invade the seed. Seedlings begin to emerge in about 2-3 weeks . The first leaf forms from the radicle which differentiates into a first root. The next 6 leaf to develop are all strapped shaped and this creates an equitant leaf form which is witnessed in Aloe plicatilis . The 7th leaf emerges with a keel on the outside surface which unequally divides the leaf into a short and a long side. This is the beginning of the twist which continues with all subsequent leaf to begin building radial symmetry. The following photos show plants in these various stages.
5 leaf plant with strap shape leaf in the equitant form, bilateral symmetry.
7 leaf plant with keeled outer side twisting, building radial symmetry.
12 leaf plant showing the keel with dentation . Both upper and lower leaf surfaces are photosynthetic. Note the parallel veins both primary and secondary. The leaf stores “goo” freely, not contained except by the leaf itself , and is available for transport to create new root tissue. This species is very adept at translocating the “goo” for this.
The pathogen which must be managed is Fusarium oxysporum , a primitive fungus that has a wide host range and troubles many agricultural and horticultural species. Ultraviolet light kills leaf infections, which only mar the leaf with purple lesions but do not kill the plant. Roots suffer purple lesions which are localized, and also are not fatal. Undercrown infections are very fatal to the plant. Seedlings are most susceptible and adult plants are much less susceptible unless chewing insects are at work undercrown. This photo shows how a fatal infection looks . A very coarse soil mix is recommended to stop root infection and provide enough oxygen for the roots to inflate each leaf .This is the main factor in growth . The Fusarium is intolerant of dessication. It can infect only when ‘free’ (unbound) water is present. The best management strategy is to permit soil moisture to fall to 50% capacity before applying water again. The recommended soil has little water holding capacity ; Pumice rock or perlite 2:1 potting soil by volume for 25 leaf plants. Juvenile plants should be in a greenhouse in a richer soil mix such as perlite 1 :1 soil.
Early stage Fusarium infection from undercrown. In nearly all cases like this I have found an insect in the order Collembola responsible for creating a court of infection.
Advanced stage meltdown.
Some field photos from Lesotho showing some of the largest plants
Plant division occurs frequently, requiring about 3 years to complete.
This plant has changed growth orientation from Right to Left, an uncommon observation. This says that there is no genetic fix on growth orientation.
By: Alan Beverly, Winter 2017