The following points highlight the nineteen main sculpture types that ornament both pollen and spore. The sculpture types are: 1. Chagrenate 2. Psilate 3. Spinula 4. Spina 5. Pilum 6. Verruca 7. Gemma 8. Clava 9. Baculum 10. Scabrate 11. Rugulate 12. Striate 13. Cicatricose 14. Reticulate 15. Corrugate 16. Foveolate 17. Fossidate 18. Canaliculate 19. Echinate.
Sculpture Type # 1. Chagrenate(Turkish ‘gaghri’ means un-tanned leather-Fig. 4.11A):
The term describes the surface of a pollen grain and spore that are smooth, shiny, structureless and translucent. Traverse (1988) considers the term as ‘a variant of psilate’. Individual structure particles are not recognizable.
Sculpture Type # 2. Psilate (adj., in Greek psilos means smooth-Fig. 4.11B):
The term describes a pollen grain and spore with surfaces completely smooth. The tectum is devoid of any processes. The surface appears as a mat that may have small depressions or pits that are less than one micron in diameter. Example: Aconitum, Betula.
Sculpture Type # 3. Spinula (pi. spinules, adj. spinulose-Fig. 4.9A):
This supratectal process is pointed towards apex and the length of a spinula never exceeds three micra.
Sculpture Type # 4. Spina (pi. spines, adj. spinose):
This supratectal element has pointed apex and the length of it always exceeds three micra. A spina has a broad base that narrows slowly towards apex.
Sculpture Type # 5. Pilum (pi. pila, adj. pilate – Fig. 4.10L, M & N):
Pilum is blunt and drumstick- shaped element. It has a swollen more or less round or elongated top called caput and a rod like part that holds the caput-termed baculum (Erdtman, 1952).
A pilum is taller than one micron. Caput and baculum together, apart from supratectal projections, may form sexine where the capita and bacula represent respectively ectosexine and endosexine. Example: Merciiriales, some elements of Ilex and Nymphaea.
Sculpture Type # 6. Verruca (pi. verrucae, adj. verrucate; in Latin verruca means a wart- Fig. 4.10D & E):
Verruca is a rounded projection on the tectum where the breadth, i.e. diameter of radial projection at the lower part is greater than length. The base of verruca is not constricted.
The surface of verrucae can be round, flat or irregular. In a grain the verrucae differ in shape and size. Thus in surface views round and less round verrucae are observed. The diameter of a verruca is more than one micron. Example: Plantago, Fumaria and Aristolochia arborea etc.
Sculpture Type # 7. Gemma (pi. gemmae, adj. gemmate; in Latin gemma means a bud – Fig. 4.10F & G):
Gemma is a spherical sculptural element whose greatest diameter of radial projection is greater than height. It may be more than one micron in diameter. The lower part is constricted. Example: Juniperus, Linum and some elements of Nymphaea etc.
Sculpture Type # 8. Clava (pi. clavae, adj. clavate; in Latin clava means a club —Fig. 4.10H & I):
Clava is a club like supratectal process where the length is greater than breadth. It is more than one micron in length. The apex has greater diameter than base. Clava gradually narrows towards the base. It is like a baculum where the apex is thicker than base. Example: Some elements of Ilex.
Sculpture Type # 9. Baculum (n., adj. baculate; in Latin baculum means a rod —Fig. 4.10B & C):
Baculum is rod like the length of which is much greater than the diameter. The rod is of equal thickness throughout apex and base. Each baculum is more than one micron high. It is straight and often ends abruptly. It may occur as supratectal process in tectate pollen grains. In intectate or semitectate pollen grains it may form a part of sexine, where bacula stand at right angles to nexine. Example: Some elements of Nymphaea and Viscum etc.
Sculpture Type # 10. Scabrate (L. scaber means flecked-Fig. 4.11C):
These are small sculpturing elements on the surface of pollen. The projections are radial and less than or equal to one micron in diameter. The shape may vary. This term is also used synonymously with granulate. It is a general term for all elements that are less than one micron in diameter. Example: Artemisia campestris, Quercus, Populus, Urtica etc.
Sculpture Type # 11. Rugulate (L. ruga means a wrinkle, L. rugolosus means ‘covered with creases’; L. rugulae, sing, rugula; Erdtman, 1969-Figs. 4.11 D & 4.12):
The surface of a pollen grain and spore is provided with radial projections, the length of which is at least twice the breath. The ridges are irregularly distributed over the surface. Rugula appears long and narrow in surface view. Example: Nymphoides peltatum, megaspore of Selaginella densa (Tschudy etai), Botrychium australe, Sedum, Ulmus, Apium and Erodium etc.
Sculpture Type # 12. Striate (L. stria means striped-Figs. 4.11E & 4.12):
The surface of a pollen grain is provided with ridges and grooves. The ridges and grooves are numerous, more or less parallel to each other in the exine. The sculpture elements form linear or ‘fingerprint’ like pattern and thus exhibit parallelism. The striate ornamentation may also be referred to as muri and grooves.
The sculpturing elements are elongated sideways and the length is at least two times greater than breadth. In striate pattern muri/ridges are sometimes called valla (sing, vallum) or lirae (sing, lira). The inter-ridge spaces are ‘streak-like furrows’ termed striae (sing, stria, streak; Erdtman, 1969). Grains having striae are described as striate pollen. Example: Menyanthes, Saxifraga, Potentilla, Gentiana and Helianthemum etc.
Sculpture Type # 13. Cicatricose (L. cicatrix means a scar- Fig. 4.11F):
The surface of a pollen grain is provided with stripes or ridges. The ridges run more or less parallel in the manner of a fingerprint over the surface of grain for a long distance. The stripes are not arranged in a net. The ridges are narrower than the spaces that separate them. Example: Anemia phyllitidis, Cicatricosisporites.
Sculpture Type # 14. Reticulate (L. rete means net-Figs. 4.6E, F, 4.11K & L, 4.9B):
The surface of a pollen grain is provided with ridges. The ridges anastomose and form reticulum that may be irregularly polygonal or regularly hexagonal. The ridges, also termed muri, are narrower or equal than the spaces they enclose. The enclosed space is termed as lumen (pi. lumina). Lumina are more than one micron in diameter. Example: Fritillaria, Potamogeton, Hedera and Cruciferae.
Sculpture Type # 15. Corrugate (L. corrugatus means wrinkled – Fig. 4.11G):
The surface of spores is provided with projections or ridges. The ridges are with regular or irregular bulges or radial humps. Example: Riccia natans (Tschudy et al).
Sculpture Type # 16. Foveolate (L. fovea means a pit-Figs. 4.11H & 4.12):
The surface of a spore is provided with more or less circular pits. The diameter of pit is equal to or more than one micron. Sometimes the lumina or cavities may be up to two micra in diameter, or if larger, are too widely separated to form a reticulum. The spaces, i.e. the ridges that separate the pits are wider than the diameter of pit. Foveolae are larger than scrobiculae. Example: Lycopodium phyllanthum, L. selago, Tilia and Fagopyrum etc.
Sculpture Type # 17. Fossidate (L. fossa means a ditch-Fig. 4.11I):
The surface of spore is provided with grooves. The grooves are irregular on the surface and do not anastomose. They may be straight or sinuous. The grain has a reticulate appearance. The boundary of the reticulum is formed by grooves.
The spaces between the boundary are elevated sexine elements. Such reticulum is described as negative reticulum. A true reticulum differs in having ridged muri and the depressed lumina. Example: Pteris tripartia, Ledum palustre and Huperzia selago.
Sculpture Type # 18. Canaliculate (L. canalis means a channel —Fig. 4.11J):
The surface of a spore and pollen grain is provided with channels or cavities. Raised stripes occur between the channels. The cavities or channels are narrower than the raised stripes that separate them. Example: Anemia simii (Tschudy et al).
Sculpture Type # 19. Echinate (L. echinatus means prickly-Fig. 4.10J & K):
This term describes a pollen grain with echinae. Echinae are processes that have broad base that tapers towards apex to a sharp point. They may vary from cylindrical to cone-shaped. The processes are more than one micron high. The term is used as a synonym of spina. Example: Taraxacum, Malva, Cirsium and Lonicera etc.
In describing sculpture, it is customary to record the size range of sculptural elements. This includes height and breadth of spinae, verrucae etc. In describing reticulum, diameter of lumina and the width of muri, shapes of lumina (polygonal/rounded/hexagonal etc.) together with the nature of sides (converging/diverging/parallel etc.) are to be recorded.
The ornamentation can be grouped into two broad categories, namely Excrescence type (e.g. ehinate, baculate and gemmate etc.) and Depression type (e.g. foveolate, scrobiculate and fossulate etc.). Nair (1970) discussed about the relative primitiveness of the two types and concluded that ‘the two categories represent two parallel lines of morphological evolution’.
Faegri et al. formulated a key to identify some common sculpturing types, which are reproduced in Box 4.1.
It is regarded that the sculpturing of exine of a pollen grain has functional significance. It is expected that the conspicuous processes that occur on exine are associated with adhesion to pollination vectors. It is assumed that pollen grains with psilate exine are anemophilous whereas the grains with other sculptured exine are entomophilous.
But this is not applicable in all cases. As for example, pollen grains of Araceae have psilate, echinate, verrucate, striate and reticulate exine. It is observed that the psilate grains are pollinated by slow moving beetles. The psilate grains get stuck to the smooth surfaces of pollinators with the aid of sticky secretions from the stigmas.
A few entomophilous pollen grains of Araceae have their own adhesive materials, referred to as pollenkitt that is not evident in acetolysed pollen. The echinate grains are largely pollinated by flies and it is regarded that such grains are better adapted for attachment to the hairy bodies of fast-flying flies. For more details consult Grayum (1986).