Macrophotographs were taken with a Canon A300 digital camera, with a resolution of 1024 x 768 pxs. and trimmed or reduced to fit them to this article. The photomicrographs were taken from sections made with a mesotome, using my National Optical microscope, with planachromatic optics and an integrated digital camera of 0.4 Mpx, at 640 x 480 pxs. Backgrounds were cleaned, pictures were trimmed, or mosaics were made to reconstruct organs, using PhotoPaint. I believe that the illustrations on the two articles of this illustrated monograph of Aptenia cordifolia, clearly shows the utility that the mesotome can have in fast researches on certain plants and, mainly, in teaching botany.

 Key words: Aizoacea, Aptenia cordifolia, mesotome, teaching botany

THE FLOWER

 
Aptenia N.E. Brown, is a genus pertaining to the Aizoacea Family.

Aptenia cordifolia (LF) Schwante, the better known species, has a long history. It was first described by the son of Carolus Linnaeus, the so-called Father of Systematics that dominates the scene of the classification of living beings still today, in spite of important new concepts that probably will impose a more modern version to supplant it.

For those who need to refresh on the basic elements of the taxonomic categories, references were given in the first article on this species. As it is usual, different authors interpret some facts in a different form, and that causes some species to be been assigned successively to several genera. The following one is a list of the known names for Aptenia cordifolia.

The letters between parentheses (L.f.) refers to the first author who described the species and means Linnaeus filius, son of Lineo, also known as Carolus Linnaeus. In his time he also was an important botanist, eclipsed by the enormous importance of his father.

 Aptenia cordifolia (L.f.) Schwantes

Synonyms

Litocarpus cordifolia (L.f.) Bowl.L.

Tetracoilanthus cordifolius (L.f.) Rappa & Camaronne

 A scientific description of the flower of Aptenia can be read in

HTTP://www.efloras.org/florataxon.aspx?flora_id=1&taxon_id=102363

But, as we did with the vegetative organs, I prefer to present the facts in graphical form.

 Magnoliopsida (which we knew before as Dicotiledoneae) are the most evolved plants. Like the mammals, which are the end of the evolution of animals, the magnoliopsida also tried successfully to protect their embryos, and their development, in special closed organs. Although, of course, with structural differences that responds to different ecological necessities, because plants are live entities fixed to the ground and developed reproductive methods to fit to that fact.

 The strategies of Aptenia, then, are the following ones:

 The plant grows thanks to the development of buttons at the end of their stems which give origin to new stems, leaves or flowers. In Aptenia it is easy to recognize the buttons which we will call "foliar" (Lb) from those that we will denominate "floral" (Fb)

Fig. 1 – the plant, (click to see the labeled photo).

Fig. 2 – Foliar button from which only stems and leaves are developed.

Fig. 3 - the floral button is distinguished because the sepals (that is to say the modified leaves that will form the calyx) are different: two are more or less similar to normal leaves, but the other two have the form of a horn or claw, thin and curved. The beginning of a handful of red petals appears in the junction of the sepals.

Fig. 4 - the flower develops directly, and it opens with the light of the day.

Fig. 5 - At night the flower is closed. (Note: as a reference to this characteristic, Mesembrianthemum, the genus to which the plant was originally ascribed, means "midday flower".)

Fig. 6 - My plants generate two types of flowers: sterile ones, (see fig.4) without visible stamens; the others are complete and fertile. By its symmetry this is an actinomorphic flower and because it has all the sexual organs (masculine and feminine) it is denominated a perfect flower. By counting, assigned to the flower are 140 elements of the corolla including petals and staminodes (see picture 7).

It is a weird thing that in my plants (and those of some other gardens in Cancún) only approximately 1 of each 5 or 6 flowers is a perfect flower, the others show only petals and staminodes.

Fig. 7 - (Click to see the labeled picture.) The corolla has many layers of petals (Pt) in whose interior several circles of stamens with yellow anthers (St) are seen. Outside the normal stamens there are some circles of stamens without anthers (they only show the filament) that are denominated staminodes (ET). This photo was taken using the “Köhler microscope" previously described, with the Obj. X 4.

Fig. 8 - a lateral view of the flower shows that the 4 sepals over the petals (together, sepals and petals form the corolla) fuse to form the more or less conical receptacle or hypanthium in which the feminine organs or carpels lodge (a carpel is the set of the ovary, style and stigma). In this flower the carpel practically does not have a "style", (see figs. 9 and 12).

Fig. 9 - a longitudinal section of the immature flower shows in more detail the relations of all these elements. (Click to see the labeled image), petals, Pt; stamens, St; stigma, st; 2 carpels, c1 and c2, are shown in the section; ovules, ov; and receptacle, R). The set of photographed elements constitutes what it is denominated the perianth.

Petals and sepals were trimmed to allow a better dissection. It's evident, of course, that the section has left out the pedicel or short stem on which the flower develops.

Fig. 10 - The stamens join together at its base (obj. X 40, il. top light).

Fig. 11 - the staminodes, has only the filament, without the anther.

Fig. 12 – the stigmas are practically seated at the ovary’s end, without a style.

Fig. 13 - the stamen filament has a package of nourishing vessels, and the anthers are developed in its end, as a double sac. Obj. X 10, Darkfield.

Fig. 14 – on maturing anthers develops the pollen grains, where the male cells are lodged. Normally, once mature, the anthers in this flower open by one longitudinal dehiscence furrow. This anther is not yet mature as to open itself, the pressure of the coverslip has broken its envelope. Obj. X10, Darkfield.

Fig. 15 - the pollen grains seen with the Obj. 40x, brightfield.

Fig. 16 - several types of pollen grains present in the same slide. Obj. 100x HI, Stained with Fast Green, mounted in Glycerin Jelly.

Fig. 17 - 1, 2, 3, three planes of the same pollen grain. 4, 5, two planes of another one. 6, a very different geometry. Obj. X 100, Immersion, Brightfield.

 Results were the same, although the punctuated nature of the exine could be better observed. Proportionally only a few pollen grains showed a normal shape.  As  seen in fig . 16 (2 and 5)  and in this mosaic, the viable pollen grains are tricolpate. ( Many thanks to Andre Advocat from the French Forum Microscopies  for the  determination.)

Fig. 18 - most of the pollen grains (taken from 3 different flowers) were irregular.

 Thinking that the applied treatment (staining-fixing solution) could distort the results, I applied the same technique to pollen of Morning Glory, Ipomea purpurea, and also to the one of a small wild composite flower, whose species I don’t know. In both cases all the numerous grains gathered had not only a similar diameter but also identical morphology.

Fig. 19 – At left, the pollen of Ipomea purpurea, a little squashed by the coverslip. At right the pollen of a small wild composite, of unknown species. Both with the 40 x Obj.
 

Adding this fact to the low incidence of fertile flowers, it occurred to me, without any certainty, because I am not a trained botanist, that this may be due to the fact, reported in the following article on the Internet, and elsewhere, that plants known as the red variety of Aptenia cordifolia, can be really a hybrid cultivar.

 HTTP://www.mediterraneangardensociety.org/plants/Aptenia.cordifolia.cfm

The most commonly grown plant, usually grown under the cultivar name of 'Red Apple', is considered by some botanists to actually be a hybrid between Aptenia cordifolia and the closely related Platythyra (Aptenia) haeckeliana. It certainly shows the vigor common among bi-generic hybrids, carpeting large areas easily in a season or two.

Fig. 20 - Once fertilized the flower closes its petals, which will dry and fall, and start to produce the fruit. This longitudinal section of a young fruit is a mosaic reconstructed with 8 independent images. (Click the picture if you want to see a larger image.) T - pedicel; PV - Vascular package which feeds the carpels; R - receptacle, that contains the carpels; P - dry petals still adhered to the young fruit; B - sepals; OI - inferior ovary, located underneath the corolla. The flowers that have this disposition are denominated epigynous (Epi, over, ginos, the gineceum or set of feminine reproductive organs.) As it can be seen, the ovary is "submerged" in the receptacle or hypanthium. In the varied (and complicated, according to the author) botanical terminology, this is also denominated pericarpel, whereas the petals that normally are interpreted as "the flower" are over that. Obj. X 4. Darkfield Illumination

Note: carpel is the set of ovary + style + stigma. As it can be seen in figure 22 this flower has 4 fused carpels.

Fig. 21 - as it is seen in the previous image and in this longitudinal section, through two carpels, the ovules of each ovary are adhered to a central axis and lodged within a cavity denominated the locule.

Fig. 22 - this cross section at half length of the hypanthium shows that they have four locules, each one corresponding to a carpel. The anatomical elements of the ovary are better identified in the following image. Because of problems due to illumination and color variations when the section moves over the microscope stage to produce the images needed for the mosaic, this one required 11 different pictures. The original image was 1316 x 1282 pxs. Obj. X 4, Rheinberg Illumination

Fig. 23 - Each future seed is bound to the axis by a filament or funiculus, adhered by its base to a placenta, and with the future seed in the other end.

(Click to see a labeled picture.) E - central Axis; PC placentae; F - funiculus; Ov - ovules; Sp - septum separating two locules; End.- endocarp, inner wall of the locule; Pr - pericarp or wall of the ovary; Ec - Ectocarp, external covering of the ovary; Hz - beams or vascular packages that feeds the pericarp. Mosaic of two images.

Fig. 24 - the zone of insertion of the funiculus in the placenta. X40, Darkfield.

Fig. 25 – a locule cross-section. As it were seen in the 17 picture, the ovules are adhered over the whole length of the axis. This style of placentation is named axial placentation. Mosaic of two images.

Fig. 26 - the mature seed accumulates food around the embryo and protects the total adding a hard outer layer, provided with superficial tubercles. In this figure an almost mature seed can be seen.

Mature carpels produce the fruit. In the consulted electronic bibliography the fruits of Aptenia are named capsules, a fruit type common in the Aizoacea.

But the appearance of the fruits of my plants (see Figs. 28 and 29) are more similar to a "pome", a type of fruit in which the pericarp thickens, becomes succulent, and holds the seeds in a reduced central space. It is interesting that the best example of this last type of fruits is the apple.

Fig. 27 - aspect of the mature fruit in the plant.

Fig. 28 - fruit with the rest of the sepals and petals peeled off. There are seen the 4 stigmas corresponding to the 4 carpels.

Fig. 30 - a seed cut by the mesotome, showing in its contour the characteristic superficial tubercles.