3.1.1. Seedlings
The germination in Kissenia capensis is epigeal. The cotyledons are oblong, with entire margins, inconspicous venation and are amongst the largest of any Loasaceae. Although the terminal hydatode tooth common in other Loasaceae (Weigend, 1997) was not observed, the base of each cotyledon blade has two small gland-like structures on either side of the petiole insertion. The first few pairs of leaves produced after the cotyledons are opposite, with ovoid to rhomboid, entire blades, irregularly dentate to crenate margins and subpalmate leaf venation(Fig. 1A). By the third pair of leaves produced after the cotyledons, the lamina is lobed. By the fourth pair of leaves, the phyllotaxis switches from opposite to alternate. In these early stages, the leaf blades are generally larger than is common in most adult plants, being almost as long as wide and with a well defined cordate base (Fig. 1B).
3.1.2. Adult habit
Mature plants in the wild tend to be densely branched, sometimes hemispherical shrubs (Figs. 2A, 3A), but their size is variable and probably dependent on the kind of substrate
76 Chapter 4 – Taxonomy of Kissenia and moisture available in their habitat. Some individuals may start producing flowers at about 30 cm in height, and old plants can be over 1.2 m in height. The wood anatomy of Kissenia capensis was studied by Carlquist (1984) who mentions it bears resemblace to Nasa picta (Hook.) Molinari and Presliophytum incanum (Graham) Weigend, the other loasoids he analyzed. This species has abundant diffuse axial parenchyma and relatively large multiseriate rays. Like other deserticolous loasoids (Huidobria Gay, Presliophytum (Urb. and Gilg) Weigend), Kissenia species exfoliate their epidermis, that turns whitish, as the periderm starts to develop. Kissenia also has a well developed taproot. Mature plants seem to be at least partially deciduous in the wild. The plants studied in cultivation
Fig. 1. Distinctive morphological traits of Kissenia. A. Kissenia capensis seedling, about one month old, cultivated at the Botanical Gardens of the University of Bonn. Notice the opposite phyllotaxis, the ovoid leaf laminas and the oblong outline of the relatively large cotyledons under the youngest pair of leaves. B. Older young plant of Kissenia capensis in its natural habitat in Namibia. The relatively wide pentalobate leaf laminas with a well-defined cordate base are common in plants before their first reproductive cycle. C. Ovoid, trilobate leaf, from a fully mature, reproductive Kissenia capensis plant, cultivated at the Botanical Gardens of the University of Bonn. D. Overview of the abaxial leaf indument of a fully mature leaf of Kissenia capensis, obtained from a plant cultivated in the Botanical Gardens of the University of Bonn.
Besides their length, there is little variability in trichome morphology. E. Detail of an area between the veins from the same sample as (D). F. Indehischent capsule of Kissenia capensis taken from its natural habitat in Namibia. The sepals are persistent and remain attached to the fruit even after it has fallen from the parental plant. Notice the long, smooth tricomes that cover the outer walls of the capsule in row. Scale bars = 300 μm. Credits B. by Norbert Jürgens.
F. by Meredith Cosgrove.
Chapter 4 – Taxonomy of Kissenia 77 became leafless during the winter months for three consecutive years, flushing new leaves each spring.
3.1.3. Leaf morphology
Although the first few pairs of leaves produced by the seedlings are opposite, these are shed in few months. By far, most of the leaves produced in a lifetime are alternate.
Mature plant leaves are petiolate, amphistiomatic, with the blades ranging from from narrowly ovate to subcircular, usually tri to pentalobate, with a cuneate, truncate or shallowly cordate base (Fig. 1C). In general the leaves of K. capensis are narrower and with deeper incisions in the blade, while the leaves of K. arabica are wider with shallower incisions, but there can be significant variation in morphology, even within a single plant, depending on the season, sun exposure, soil moisture and age of the plant.
Because of this, differences in leaf blade size and proportion are not always clear cut between both taxa and telling apart some plants without examining locality data or the nectar scales would prove problematic.
3.1.4. Indument
The plants are densely covered with rough, scabrid and glochidiate trichomes (Fig. 1 D,E). These are by far the commonest kind of trichomes that have been observed in Kissenia, a similar situation to its potential closest relatives: Huidobria and Klaprothieae.
This constrasts with the rest of the subfamily, that frequently have abundant stinging and/or glandular trichomes (Weigend, 1997, 2004). The density of the indument causes the foliage to look powdery or greyish (Fig 2 B, 3B). The trichomes on the stem, petioles and over the abaxial veins in mature leaves, measure up to 1 mm long (Fig. 1D) while adaxially and abaxially between the veins, they measure to 500 µm long (Fig. 1E). The differences in trichome structure adaxially and abaxially as well as over and between the veins are minor, not taking into account their length. The ovary and fruit outer walls are covered by much longer (ca. 5 mm), whitish to golden yellowish, smooth trichomes (Fig.
1F), that at least in dry specimens could cause skin irritation, especially near the insertion of the sepals. The ontogeny of these trichomes and their affinities with the trichomes of other Loasaceae have not been studied.
78 Chapter 4 – Taxonomy of Kissenia 3.1.5. Inflorescence morphology
Inflorescences are cymoids with monochasial branches and alternate bracts. The last are morphologically very different from vegetative leaves, being significantly narrower, sessile, with entire, lanceolate blades and entire to slightly undulate margin. Due to these differences, it is straightforward to distinguish vegetative from reproductive branches.
The bracts show concaulescence and recaulescence and of each bract pair (on rare occasions could be more than one pair of bracts per flower), usually one is concaulescent and is attached to the flower pedicel (a trait apparently unique to Kissenia in Loasaceae, Weigend, 1997), while the other is recaulescent and inserted near the pedicel of the next flower. Although there is overlap in their sizes, the bracts of K. capensis can occasionally grow significantly wider than those of K. arabica. The flowers are erect.
3.1.6. Flower morphology
The flowers in Kissenia are epigynous, pentamerous, actinomorphic and complete (Figs.
2C, 3C. The sepals are oblong to obovoid, usually slightly wider terminally than proximally, with three conspicuous main veins along their length (two more can be seen often near the base). These are 2–3x longer than the petals, and elongate further after anthesis. The corolla aestivation in Kissenia is imbricate, as in Huidobria Gay, Aosa grandis (Standl.) R.H.Acuña and Weigend and several bird pollinated species of Nasa Weigend. The petals are half- to full-spreading, cymbiform, white to cream, with a well-defined claw and limb. The floral scales are antesepalous, lanceolate, formed by three fully fused staminal primordia (Hufford, 2003) and lack dorsal threads. These are mostly the same color as the petals, however the base of the neck is adaxially brighter yellow.
The apex of the neck is elongated and transformed into a ligule (Fig. 3 C), which folds over the nectar scale back (both species), and then again distally near the tip (K.
capensis). The presence of a ligule-like structure is unknown in other loasoids, and it may be lamelliform and have an entire or shallowly lobed to cleft apex (K. capensis) or be thread-like, either undivided or deeply divided into 2 (-3) irregularly twisted filiform appendages (K. arabica). Adaxially, opposite to the nectar scale there could be two or four free staminodes. The central two staminodes are always present and their base is conspicuously flattened, with a flange directed towards the scale; the area above the
Chapter 4 – Taxonomy of Kissenia 79 flange is filiform with a flattened or clavate tip. If four staminodes develop the lateral pair could have sterile anthers and be intermediate in morphology between the central staminodes and fertile stamens. There are ca. 40–80 fertile stamens per flower, usually arranged in 5 groups opposite to the petals. These have a filiform whitish filament and yellow anthers with semi-circular thecae. The style is ca. 5 mm long and has 3 stigmatic lobes, twisting after anthesis. The ovary is pubescent, asymmetrically bilocular, with two placentae (one on per locule), each with 1–2 anatropous, pendulous ovules (Urban and Gilg, 1900). However, some authors consider the ovary to be actually unilocular, due to the septum apparently not dividing entirely both locules (Weigend, 1997).
3.1.7.Fruit morphology
Fruits are erect, inferior, straight, indehiscent, ligneous capsules, ellipsoid to globose-cylindrical, 5–7 mm in diameter with persistent, post-anthetically elongated, oblong to obovate sepals (Figs. 1F, 2D, 3D). Like the ovaries, the mature capsules are covered by long, yellowish to golden smooth trichomes, ca. 5 mm long. Each capsule usually has 2 seeds. The greatly elongated sepals are probably an adaptation for anemochory (the fruits being the dispersal, not the seeds as in most Loasaceae).
3.1.8. Seed morphology
The seeds are oblong, exalbuminous, yellowish, with a thin, reticulate testa and fill most of the volume of their respective capsule locule. Most of the seed itself is made up of the embryonic cotyledons (Urban and Gilg, 1900; Weigend, 1997).
3.2. Distribution and habitat
Kissenia is a deserticolous genus. Both species are widely disjunct geographically from each other, with one species restricted to southwest Africa (western Namibia and northwest South Africa) and the other to northeast Africa (Djibouti, northeast Ethiopia, northern Somalia) and southern Yemen (Fig. 4). They grow in desertic to semidesertic areas between sea level and 1400 m, on granitic, calcareous, quartzitic or basaltic gravel or sand, often in areas with large exposed rocks, such as mountain slopes, kopjes, dry
80 Chapter 4 – Taxonomy of Kissenia riverbeds (wadis), alluvial plains, cliffs and gorges. Both species could be common locally, even near settled areas or roads.
3.3. Pollination ecology
The flowers have showy pale corollas and nectar scales that can accumulate enough nectar to overflow them (at least in cultivation: obs. pers.). The latter also have necks that are slightly contrasting in color. These traits suggest some form of entomophily, although pollinators have not been reported so far in the literature. Ants have been observed visiting both species (photo by Ina Dinter: Dressler et al., 2014–Ongoing; Fig. 3B), but whether they are just nectar robbers or actual pollinators has not been assessed.