Studies in the southern African species of Justicia and Siphonoglossa ( Acanthaceae ) : palynology

The gross morphology of the pollen of all southern African species and subspecies of Justicia and Siphonoglossa was investigated, as well as that of eight tropical African species of Justicia. The following pollen types were found in the southern African species of Justicia: twoor three-colporate, each with the margocolpus either entire or broken up into areolae, and two-porate areolate pollen. One tropical African species had the colpus very short, and in another tropical African species it was replaced by an extra row of areolae. All Siphonoglossa species had two-colporate pollen with areolae and long colpi. The southern African species of Justicia could be separated from Siphonoglossa on pollen characters, and some sections of Justicia could also be distinguished on the same basis.


INTRODUCTION
The gross morphology of the pollen of all southern A frican sp ecies and su bsp ecies o f J u sticia and Siphonoglossa was investigated, as well as that of eight tropical African species of Justicia.In order to place the studies into perspective, brief reference is made to findings o f other researchers.Radlkofer (1883) was the first to point out the potential value of the pollen in classification o f the Acanthaceae, but it was Lindau (1895) who first attempted to use the pollen systematically in its classification.
The 'typical representatives' of the subtribe Justiciinae, according to Bremekamp (1965), have prolate, dorsiventrally flattened pollen, with the pore in the middle of a trema area which is studded with circular 'insulae' (areolae).Stearn (1971), after discussing the pollen type o f a number of Jamaican species of Justicia, concluded that T h e palynology o f the group as a whole must certainly have a significant part in its reclassification.Pending that reclassification, Justicia is probably best accepted in a broad sense'.Gibson (1972) widened the circumscription of Justicia and, it her delimitation is accepted, the range of pollen types present in the genus will be greatly increased, and will include 3-and 4-porate pollen and pollen with the areolae scattered across the face o f the grain.Balkwill & Getliffe Norris (1988), who reappraised the tribal and subtribal limits o f Acanthaceae in southern Africa, considered that in southern Africa each tribe had a characteristic pattern of pollen 'against which aberrant genera can be contrasted'.They considered prolate tricolporate grains with entire margocolpi as being the primitive state.Graham (1989) surveyed a number of species o f Justicia and related genera worldwide, and greatly widened the circumscription of the genus to include a number of formerly segregate genera, including Siphonoglossa.She divided the genus into a number of sections and subsec tions which have been followed here, and considered pollen, in combination with other characters, to be of major taxonomic importance.She considered the South African species of Siphonoglossa to belong in Ju sticia, but not in the same section as the South American spe cies o f Justicia.She described 10 pollen types, but did not confirm the 4-aperturate pollen types reported for a few New World species.

METHODS AND MATERIALS
In this study the pollen of all southern African species and subspecies of Justicia and Siphonoglossa was investigated with the SEM.Taxa covered were all those occurring in southern Africa as defined by the Flora o f southern Africa.Eight tropical African species were also investigated for purposes of comparison, but were not measured.

RESULTS AND DISCUSSION
N o differences were observed between pollen taken from fresh and from dried material when it was viewed.
N o significant difference was found between acetolysed material and material mounted directly onto the stubs.This is similar to the findings of Munday (1980) in M onechma, except that acetolysed material tended to loose its 'stopples' and had a high proportion o f damaged grains.Material was therefore viewed throughout without pretreatment, and results given are o f such pollen.

Shape o f pollen grains
The pollen o f both Justicia and Siphonoglossa was found to be basically prolate, with some species, e.g.J. orchioides L. f., J. platysepala (S.Moore) P.G.Mey. a n d / thymifolia (N ees) T. Anders., showing a slight median constriction (Figure 5C).

Sexine pattern
The In the case o f pollen with entire paracolpoid ridges, the colpoid streak (which appears as a furrow between the paracolpoid ridge and the main area o f lophate sexine) would sometimes continue to the poles.This, however, may be variable (see also Balkwill & Getiiffe Norris 1985), and has not been used in the classification.The pseudocolpi may actually join at the poles, for instance in J. campylostemon and J. glabra among the threecolporate species (Figure 2D ).

Pores and colpi
The pollen grains have either two (Figures 4 & 5) or three pores (Figures 2 & 3).Each may lie within an elongate colpus running to near each pole.It is sometimes difficult to establish with certainty whether there is a colpus or not.Two species, however, J. anselliana (Nees) T. Anders, and J. anagalloides (Nees) T. Anders., were definitely without colpi (Figure 4G).An intermediate stage was seen in one o f the tropical species, J. elegantula S. Moore, where the colpi were present but short.Another tropical African species, J. g oetzei, had a single row of areolae where the colpus would normally be.In all species a granular stopple was present projecting from each pore (Figure 4B, C).Size (length) o f pollen grain, although used in the key below, has not been used to reach taxonomic decisions, as there is a large range in pollen sizes in each species, even in measurements taken from a single flower.Keys using pollen sizes would need to be drawn up with caution, and be based on a number of pollen samples from different individuals and populations.

Abnormal grains
These are seen occasionally in both genera, and take the form o f a much larger than average, triangular grains with a trilete colpus (Figure 5F).It is presumed that these are what Bhaduri (1944)   The South African species of Siphonoglossa had twocolporate pollen with areolae and long colpi.On the basis o f the pollen characters the genus would seem to most resemble Justicia sect.H am ieria.
sexine pattern was lophate or reticulate over most o f the grain with smooth areas (margocolpi) on either side o f the colpi.These margocolpi were ornamented either with an entire band o f lophate sexine (paracolpoid ridge) (Figure 1A) or this band was broken up into areolae, i.e. circular areas o f lophate sexine (Figure IB).The areolae were in one or two rows (Justicia) (Figure 3A; 4D, G; 5A) or sometimes in up to three rows (Siphonoglossa).The outer row was frequently partially merged with the main area o f lophate sexine.In one tropical African species, J. goetzei Lindau, the area normally occupied by the colpus was occupied instead by a single row o f areolae, as well as the row on either side, i.e. a total of three rows of areolae in the pair o f margocolpi.