Starch Grains of Endosperm in Grass Systematics

Bot. Mag. Tokyo 75: 377-383 (October 25, 1962)

by Tuguo TATEOKA* ReceivedJune 19, 1962

During the past 80 years occasional attention has been paid to the structural features of starch grains of endosperm in connection with the systematic grouping of grasses. Harzl' was the first to recognize that different types of starch grains have a systematic value. He disclosed that the starch grains of grass endosperm can be divided into three types : compound grains, flat simple grains with round or elliptic shape, and simple spherical grains with or without angles. Harz believed that natural tribes should be uniform as to the features of starch grains, and referred even to the parallel development of morphological characters. The starch features were taken up by Hackel2', Krause3' and Hayek4' in their discussion on grass systematics or evolution, although Harz's division into three types was replaced by a simpler division into two types, simple and compound. Avdulov5' carefully reviewed the features of starch grains appearing in the preceding papers and compared them with his cytological findings. Avdulov discovered that the features of starch grains are not always exactly correlated in the major taxonomic groups (subfamilies) with other basic characters of systematic significance which he studied; those of chromosome number and morphology and of leaf anatomy. Therefore, Harz's and Hayek's suggestions were not accepted. Nevertheless, Avdulov advocated that the starch features have some value in systematics and used them in the subdivision of the subfamily Poatae. The opinion that natural tribes are uniform as to starch features was not upset. Starch grains of several controversial grass genera were examined by some sub- sequent investigatorsfi-8' when they studied the affinities of the species of those genera. A few recent authors9-11' also examined the starch grains of some particular groups as a part of their taxonomic studies. The conclusions of these authors were based upon the assumption that two types should be recognized in the starch grains of grass endosperm and that the festucoid grasses (except Triticeae, Bromus and Brachypodium) and the eragrostoid grasses possess compound grains., whereas the panicoid grasses, as well as Triticeae, Bromus and Brachypodium, have simple grains. Stebbins and Crampton'2', who discussed the significance of various characters used in the systematics of Gramineae, estimated the structure of starch grains as the character moderately important. No comprehensive survey of starch grains of grasses has been made after Avdulov5', however. Some contradictory results to this common opinion were obtained by the present author and were reported in Japanese13-r4'. These preliminary studies suggested that the common opinion regarding the relationship of starch grain structure to :systematics might depend on insufficient observations or adjustment of the data to non-phylogenetic system. Although starch grain data from a total of 424 species were given in Avdulov's6' list, there was a natural overemphasis on the Festucoideae. Moreover, in Panicoideae the records of starch grains appearing in Avdulov's list demonstrate that some panicoid grass species do not have simple starch grains. The present author's preliminary studies further suggested that the starch grains of * National Institute of Genetics, Misima. 878 Bot. Mag. Tokyo Vol. 75 grass endosperm could be divided into four types. Under such circumstances, it is desirable to examine the starch grains of many additional species and to reappraise their systematic use. The present paper is a report of such a study.

Material and Methods

The material was mostly obtained from the herbarium specimens in our herbarium, although additional samples were supplied from various herbaria, especially from the United States National Herbarium, Washington. Seeds dried more than 54 years ago are still useful for the observations of starch grains. Only matured seeds were used. They were thinly sectioned by hand with a razor blade and were stained by a drop of IKI.

Results

A total of 766 species belonging to 244 genera was examined. The following four types of starch grains were established in consequence of the present observations. Type 1 (Triticum type, Fig. 1) represents simple grains whose shape is broadly elliptic, elliptic-round, or rarely reniform. Angular grains are not included in this type. All members of Triticeae, including Henrardia, so far observed belong to this type, and the type is unique in having very minute starch grains (4-6,u in diameter) as well as medium-sized grains included among the much larger grains (30-40 ie in diameter) within the same seed. The uniformity of Triticeae as to the starch features is remarkable. The starch grains of Bromus and Brachypodium of Festuceae are also of this kind, but they deviate somewhat from those of Triticeae. Although the starch grains of such species as Bromus unioloides or Brachyodium serpentinii can hardly be distinguished from those of Triticeae, the grains of Bromus and Brachypodium are generally less variable in size.

Figs. 1-4. Types of endosperm starch grains. x400. 1, Type 1, Agropyron tsukusiense Ohwi. 2, Type 2, Panicum clandestinum L. 3, Type 3, Perotis ind ica O. Ktze. 4, Type 4, Festuca rubra L.

The starch grains of Type 2 (Panicum type, Fig. 2) are also simple, but their shape is hexagonal, pentagonal, round or rarely rectangular. Elliptic or reniform grains are not included. The grains within a cell are not very variable in size, although the grains within the cells near the seed coat are smaller than those in the cells of more inner parts. This type has been found in a large number of Paniceae, many species of Andropogoneae, a few species of Eragrosteae, Chlorideae, Pappo- phoreae, Arundinelleae and Arthropogoneae, and several other tribes: Bambuseae,. October, 1962 TATEOKA,T. 379

Unioleae, Phaenospermeae, Brachyelytreae, Garnotieae, Isachneae and Boivinelleae. The starch grains of this type are usually 4 - 10 ,u in diameter, but in some species they are larger : in Phaenosperma, Brachyelytrum, Cenchrus, Sorghum, etc. the grains are very lerge, 30 - 40 p in diameter. In Type 3 (Miscanthus type, Fig. 3), simple and compound grains appear in the same seed. The compound grains consist of a few (usually 2 - 4) granules. The compound grains which possess many granules and which are more typical within the Gramineae are completely lacking in the seed with this type of starch grains. The simple grains appearing in this type are usually round and rarely hexagonal or pentagonal. The occurrence of this type of starch grains was unknown until 1955 when the present author first reported it. Very recently, Metcalfe (in Bor150 found a similar kind of reserve starch grains in the spindle-shaped bodies in the roots of Lophatherum gracile. Type 3 is sporadic among species of diverse tribes, but it has never been observed in Festucoideae, Oryzoideae and Bambusoideae. In Panicoideae Type 3 has often been encountered, and in Eragrostoideae a few species have shown it. Ortho- clada, which belongs to Arundinoideae, also shows this type. Its simple grains are urge (15 -- 40 a in diameter), and the granules of the compound grains are also large. Type 3 found in Orthoclada is somewhat different from that encountered in other genera, since both simple and compound grains are apparently larger in size. The ratio of the numbers of simple to compound grains which appear in the same seed varies according to species. In such species as Tridens chapmanii, Thua- rea sarmentosa, Microstegium vimineum, Chrysopogon aciculatus, Themeda triandra, etc. the simple grains are more numerous than compound grains, showing similarity to Type 2. On the contrary, Gymnopogon spicatus, Digitaria adscendens, etc. have more compound grains than simple grains. In Dimeria, Miscanthus, etc. the simple and the compound grains appear to be about equally numerous. In Type 4 (Festuca-Eragrostis type, Fig. 4) only compound grains are found throughout the endosperm. This is the most common type of grass endosperm starch grains and is shared by a number of species of Eragrostoideae, most species of Festucoideae, Arundinoideae, Oryzoideae and Bambusoideae. Most species of Arundinelleae and a few species of Paniceae, Arthropogoneae and Andropogoneae also show this type. The size of grains and granules is variable according to species. The number of granules which constitute one compound grain is also variable, but is not very variable in the same seed or in the same species. Although it is impossible to sub- divide this type into several distinct subtypes with certainty, a rough division into typical grains with many granules and atypical grains having only a few granules may be allowed. Type 4, as found in Festucoideae, is almost always typical, the granules being mostly more than eight and sometimes numerous. The same is true of Type 4 encountered in Arundinoideae, although in a few species of Danthonia and Microlaena the granules are small in number, about six. In Oryzoideae, typical compound grains are found in Oryzeae and Phyllorachieae, while the compound grains of Olyreae are not typical but consist of 3- 10 granules. In Bambusoideae, Strep- tochaeta shows typical compound grains. Type 4 encountered in Eragrostoideae is mostly typical, but in various genera, such as Lophacme, Tridens, Halopyrum, Blepharidachne, Leptocarydion, Ctenium, Craspedorhachis, Zoysia and Tragus, the compound grains have a small number of granules. In Blepharidachne, Halopyrum and Craspedorhachis especially the corn- 380 Bot. Mag. Tokyo Vol. 75 pound grains consist of only 2-4 granules and clearly approach Type 3. In Panicoi- deae, both typical and atypical Type 4 starch grains have been found in a few species. Typical Type 4 is found in a few species of Panicum, Alloteropsis, Saccio- lepis, Reynaudia, Ischaemum, Apluda, Manisuris, Mnesithea, and some genera of Arundinelleae. The compound grains found in the other members of this subfamily have smaller of granules, usually 2-8. Thus, the starch grains with typical or atypical Type 4 appearance occur to some extent only according to subfamilies. Following is the list of genera examined, the number of species of each, and the type (or types) of starch grain observed in each. The systematic arrangement of genera is largely based on the system which was published by Stebbins and Crampton12', although it has been partly changed according to the present author's view. The first number, designated in italic, in parentheses states to the number of species examined ; the second number is the type of starch grains. Bambusoideae. Streptochaeteae : Streptochaeta (1, 4). Bambuseae : Pseudosasa (1, 2). Oryoideae. Olyreae : Olyra (2, 4), Cryptochloa (1, 4). Oryzeae : Chikusichloa (1, 4), Rhynclioryza (1, 4), Oryza (12, 4) Leersia (1, 4), Luziola (1, 4), Zizaniopsis (1, 4), Zizania (1, 4). Phyllorachieae : Phyllorachis (1, 4), Humbertochloa (1, 4). Arundinoideae. Ehrharteae : Ehrharta (5, 4), Tetrarrhena (2, 4), Microlaena (2, 4). Arundineae : Arundo (1, 4), Moliniopsis (1, 4), Molinia (1, 4), Lamprthyrsus (2, 4). Danthonieae : Danthonia (9, 4), Asthenatherum (1, 4), Pentachistis (1, 4), Schismus (4, 4), Lasiochloa (1, 4), Afrachneria (1, 4), Triodia (1, 4), Plectrachne (3, 4). Unioleae: Uniola (1, 2) Bromuniola (1, 2). Centhotheceae : Lophatherum (2, 4), Centotheca (1, 2), Orthoclada (1, 3), Zeugites (1, 4). Phaenospermeae : Phaenosperma (1, 2). Festucoideae.. Lygeeae : Lygeum (1, 4). Nardeae : Nardus (1, 4). Brachyely- treae : Brachyelytrum (1, 2). Stipeae : Anisopogon (1, 4), Oryzopsis (5, 4), Nasella (4, 4), Piptochaetium (2, 4), Stipa (8, 4), Achnatherum (5, 4), Orthoraphium ~1, 4). Meliceae : Pleuropogon (1,4), Glyceria (9,4), Schizachne (1,4), Melica (14,4). Brylkinieae : Brylkinia (1, 4). Monermeae : Monerma (1,4), Parapholis (1, 4). Aveneae : Avena (7, 4), Helictotrichon (2, 4), Amphibromus (2, 4), Gaudinia (1, 4), Holcus (2, 4), Dielsiochloa (1, 4), Hoeleria (2, 4), Trisetum (4, 4), Agrostis (17, 4), Calamagrostis (12, 4), Poly- pogon (3, 4), Triplachne (1, 4), Lagurus (1, 4), Scribneria (1, 4), Aira (1, 4), Deschampsia (3, 4), Periballia (1, 4), Molineriella (1, 4), Airopsis (1, 4), Limnodea (1, 4), Beckmannia (1, 4), Milium (1, 4), Alopecurus (2, 4), Phleum, (2, 4), Rierochloa (2, 4), Anthoxanthum (2, 4), Phalaris (5, 4). Festuceae : Dactylis (1, 4), Vulpia (3, 4), Lolium (7, 4), Festuca (13, 4), Hesperochloa (1, 4), Puccinellia (15, 4), Torreyochloa (1, 4), Pseudobromus (1, 4), Catapodium (3, 3), Sclerochloa (2, 4), Wangenheimia (1, 4), Nephelochloa (1, 4), Helleria (1, 4), Aulacolepis (2, 4), Gymnachne (1, 4), Briza (3, 4), Ctenopsis (1, 4), Cutandia (1, 4), Cynosurus (2, 4), Calotheca (7, 4), Poa (36, 4), Eremopoa (1, 4), Echino- pogon (3, 4), Echinaria (1, 4), Catabrosa (1, 4), Bromus (24, 1), Brachypodium (16, 1). Triticeae : Henrardia (1, 1), Elymus (7, 1), Hordeum (12, 1), Hystrix (2, 1), Agropyron (13, 1), Taeniatherum (1, 1), Heterant helium (1, 1), Secale (1, 1), Triticum (9, 1), Aegilops (18, 1), Haynaldia (1, 1). Diarrheneae: Diarrhena (4, 4). Eragrostoideae. Aristideae : A ristida (26, 4). Spartineae : Spartina (1, 4). Pap- pophoreae : Enneapogon (1, 4), Cottea (1, 4), Orcuttia (1, 2). Aeluropodeae : Aeluropus (1, 4). Eragrosteae : Eragrostis (2U, 4), Halopyrum (1,4), Ectrosia (2, 4), Redfieldia (1,4), Eleusine (1,4 ), Dactyloctenium (1,4), Pogonarthria (1,4), Tri plasis (1, 4), Apochiton (1,4), Lophacme (1, 4), Erioneuron (5, 4), Munroa (2, 4), Tridens (6,4;1, 3 ;1, 2), Blepharidachne (1, 4), Tripogon (1, 4), Trichoneura (1, 4), Leptocarydion (1, 4), Leptochloa (7, 4), Trira- October, 1962 TATEOKA, T. 381 this (1, 4), Gouinia (1, 2), Lintonia (1, 4), Kengia (1, 4), Pereilema (1, 4), Lyeurus (1, 4), Crypsis (1, 4), Sporobolus (12, 4), Ble pharoneuron (1, 4), Muhlenbergia (18, 4), Chabois- saea (1, 4). Chlorideae : Ctenium (2, 4), Microchloa (1, 4), Oropetium (1, 4) Gymnopogon (5, 3), Schoenefeldia (2, 4), Saugetia (1, 2), Enteropogon (1, 2), Craspedoraehis (1, 4), Pentarrhaphis (1, 4), Schedonnardus (1, 4), Tetrapogon (1, 4), Trichloris (3, 4), Chloris (12, 4) Boutelou(1, 4), Opizia (1, 4), Astrebla (2, 4), Buehloe (1, 4), Aegopogon (2, 4). Zoy- sieae : Perotis (1, 3), Mosdenia (1, 4), Zoysia (1, 4, , Tragus (3, 4), Monel vtrurn (1, 4). Panicoideae. Boivinelleae : Boivinella (1, 2). Isachneae : Isachne (6, 2) ; Coela- •chne (1, 2), Sphaerocaryum (1, 2). Garnotieae : Garnotia (1, 2). Arun.dinelleae : Arun- dinell a (2, 2 ; 1, 3 ; 1, 4), Loudetia (3, 4), Tristaehya (2, 4), Danthoniopsis (1, 4). Arthro- pogoneae : Arthropogon (1, 3 ; 1, 2), Reynaudia (1, 4). Paniceae : Panicum (30, 2 ; 2, 4), Lasiacis (1, 2), Brachiaria (3, 2), Paspalidium (1, 2), Ichnanthus (2, 2), Rhynchelytrum (1, 2), Tricholaena (1, 2), Melinis (1, 2), Echinochloa (3, 2), Sacciolepis (1, 4), Pseudoe- chinolaena (1,4), Cyrtococeum (1, 2), Alloteropsis (1, 4), Ottochloa (1, 2), Chaetium (1, 2), Oplismenus (4, 2), Hymenachne (1, 2), Digitaria (10, 2; 1, 3), Trichaehne (2, 2), Hylebates (1, 2), Axonopus (2, 2), Eriochloa (3, 2), Paspalum (5, 2), Pennisetum (4, 2), Cenchrus (4, 2), Anthephora (1, 2), Thuarea (1, 3). Andropogoneae : Dimeria (1, 3), Miscanthus (2, 3), Erianthus (1, 4), Spodiopogon (2, 2), Eccoilopus (1, 2), Microstegium (1, 2; 1, 3), Pogonatherum (1, 4), Ischaemum (3, 4; 1, 2), Apluda (1, 4), Phacelurus (1, 4), Manisuris (1, 4), Hemarthria (1, 2), Eremochloa (2, 2), Mnesithea (1, 4), Cleistachne (1, 2), Sorghastrum (1, 2), Sorghum (2, 2), Chrysopogon (1, 3; 1, 2), Arthraxon (1, 3 ; 1, 2), Bothriochloa (1, 2), Dichanthium (1, 2), Cymbopogon (1, 3), Diectomis (1, 2), Andropogon

Discussion The results described above do not agree with the common view regarding starch grains of grass endosperm in several respects. The observations show that the starch grains of Panicoideae are not always simple but are either simple (Type 2) or compound (Type 4) and sometimes the mixed type which is designated as Type 3. In Avdulov's (1931) list which designates the starch features of 74 species of Panicoideae, compound grains were reported for six species of miscellaneous genera of Andropogoneae and one species each of Urochloa and Arundinella, whereas other species were listed as having simple grains. This occurrence of compound grains in Panicoideae was not noticed by recent authors'°' i3', who referred to features of the grass starch grain, and seems to have been attributed to errors of observation, but such an assumption is now apparently incorrect. Likewise, in the Eragrostoideae which have been believed to possess only compound grains, Types 2, 3 and 4 are now known to occur. In contrast to the common view that members within natural groups are similar to one another as to the starch grain features, the observations described above indicate that two or three types (Types 2, 3 and 4) sometimes occur among members of the same tribe or even of the same genus: Tridens, Arundinella, Panicum, Digitaria, Andropogon, Microstegium, Chrvsopogon, Arthraxon and Ischaemum. The compound grains of Type 4 found in these taxa are often composed of a few granules and have an appearance resembling Type 3, which apparently stands as the connecting condition between Type 2 and Type 4. Thus, there is sometimes found an intergrading series from Type 2 to Type 4 in the same genus or tribe. Takagi17~ also observed simple grains (Type 2) and compound grains (Type 4) in various species of Bambuseae. These observations indicate that the differences between Types 2, 382 Bot. Mag. Tokyo Vol. 75

3 and 4 can hardly be regarded as very significant systematically. On the other hand, as to the starch grains of the members of Festucoideae, the present observations are in good accordance with previous records. A very few exceptions found there might have resulted from wrong observations or wrong records by the authors. Triticeae, Bromus and Brachypodium have Type 1 starch grains without exception. They may be the taxa whose starch grains were most abundantly examined by preceding workers. Type 1 clearly differs from the other types, although the starch grains of Bromus and Brachypodium do have rarely an appearance somewhat similar to those of Panicoideae which were referred to Type 2. Triticeae, Bromus and Brachypodium make a contrast to the related taxa in their starch features, because, as described above, the related taxa show only typical Type 4. It seems that the developmental processes of Type 1 and Type 4 starch grains are considerably different, but differences are rather slight between Types 2 and 3 and between Types 3 and 4. This assumption favors the opinion that Triticeae, Bromus and Brachypodium may belong to a somewhat differrent line of evolution from such other festucoid grasses as are represented by Monermeae, Aveneae and other subtribes of Festuceae than Brominae and Brachypodiinae. Although Bromus and Brachypodium are here retained in Festuceae according to Stebbins and Cramp- ton12', the relation of these genera to other Festuceae should be further studied along other lines of approach. It is unfortunate that the process of the formation of compound grains, the cause of the great difference of starch grains in size, etc. are still obscurelg'. The above descriptions clearly indicate that the starch grain features can not be categorized as either simple or compound, and these antithetic conditions can not be used rigorously in ~ystematics. It must be recognized, therefore, that starch grains are generally of minor significance in grass systematics, although in certain cases they are very useful. Hubbard's6' treatment of Henrardia as a member of Triticeae is supported by the results of the present studies. Likewise, Wagnon's9~ view that the starch grain is one of the most reliable characters to separate Bromus from Festuca is endorsed by the present studies. Since Type 4 starch grains are prevalent in Gramineae, especially in primitive taxa, such as Streptochaeteae, Arundineae, Oryzeae, etc., it is likely that that is the primitive type of starch grains in the Gramineae. The Type 1 starch grain of Triticeae, Bromus and Brachypodium and the Type 2 of Panicoideae and of a few species in other subfamilies may, therefore, be derived conditions within the family.

Summary

1. Starch grains of endosperm of 766 grass species belonging to 244 genera have been examined. The starch grains are divided into four types. Type 1 represents simple grains which are broadly elliptic, elliptic-round, or rarely reniform. Starch grains of Type 2 are also simple, but they are hexagonal, pentagonal, round, or rarely rectangular. In Type 3, both simple and compound grains are included in the same seed. In Type 4, only compound grains are found throughout the endosperm. 2. Type 1 is found only in Triticeae, Bromus and Brachypodium. Type 2 is observed in most species of Panicoideae, some members of Eragrostoideae, Arun- dinoideae and Bambusoideae and Brachyelytrum of Festucoideae. Some species of October, 1962 TATEOKA, T. 383

Panicoideae, Eragrostoideae and Arundinoideae have shown Type 3. Type 4 is most common in grasses, and is found in many species of Festucoideae, Eragrostoideae and Oryzoideae, and in some species of Panicoideae, Arundinoideae, and Bambusoi- deae. 3. Systematic significance of starch grains has been discussed. The differences between Types 2, 3 and 4 may be of minor value, as all of these types are sometimes found in species of the same genus. The difference between Type 1 and Type 4 seems to be systematically significant. According to the habitual division of the starch grains of grass endosperm into two types, simple and compound, the starch features can not be rightly used in the systematics.

I am very grateful to Dr. W. V. Brown, University of Texas, who kindly examined the original manuscript and corrected its English.

References

1) Harz, C. O., Linnaea 43: 1 (1880). 2) Hackel, E., Nat. Pflanzenfamilien II, Teil 2 (1887). 3) Krause, E. H. L., Beih. Bot. Zentralb. 25 (2) : 421 (1909). 4) Hayek, A., Oster. Bot. Zeit. 74: 249 (1925). 5) Avdulov, N., Bull. Appl. Bot. Genet. Suppl. 44: 1 (1931). 6) Hubbard, C. E., Blumea Suppl. 3: 10 (1946). 7) Bor, N. L., Kew Bull. 1950: 385 (1950). 8) Potztal, E., Bot. Jb. 76: 134 (1953). 9) Wagnon, H. K., Brittonia 7: 415 (1952). 10) Potztal, E., Bot. Jb. 75: 551 (1952). 11) Hansen, I., and Potztal, E., Bot. Jb. 76: 251 (1954). 12) Stebbins, G. L., and Crampton, B., Recent Advances in Botany Vol. 1: 133 (1901). 13) Tate- oka, T., J. Jap. Bot. 29: 341 (1954). 14) - , ibid. 30: 199 (1955). 15) Bor, N. L., The Grasses of Burma, Ceylon, India and Pakistan, Pergamon Press, London (1960). 16) Stebbins, G. L., Amer. J. Bot. 43: 890 (1956). 17) Takagi, T., Hokuriku J. Bot. 6: 106 (1957). 18) Nikuni, J., The starch handbook, Asakura-shoten, Tokyo (1961).

摘要

館岡亜緒:種子でんぷん粒とイネ科の系統分類

種子でんぷん粒がイネ科の系統分類において意義のある形質であることは,古くから認められてきたことであるが,筆者は古くから信ぜられてぎた見かたにあわない事実を見いだしたので,この形質を244 風766種について再検討した.その結果,イネ科の種子でんぷん粒には次の4型が認められることが明らかになった. 第1型(コムギ型)は,単粒で,その形は円形～だ円形,まれにじん臓形で,1細胞中に大小さまざまの粒がみられるものである.第2型(キビ型)は単粒であるが,その形が通常角ばっており,また1細胞中での大きさの変異がはげしくないものである.第3型(ススキ型)は,単粒と複粒の両方が1細胞中にでてくる型であるが,その複粒はそれを構成する粒子(granule)の数が少なく,典型的な複粒とは異なるものである.第4型(ウシノケグサースズメガヤ型)では,細胞中のすべてのでんぷん粒が複粒のもので,その複粒は通常たくさんの粒子からなっている. 多くの属では,種類によって種子でんぷん粒が異なることはなく,すべての種類が例外なしに上述の4 つの型のいずれかを示す.しかし,第3型は明らかに第2型と第4型の中間的なもので,まれにその3っの型が同一の属のな:かにみられることがある.また,その3っの型がでてくる族は相当数ある.この点から,第'2型,第3型,第'4型の間の差異は大きな分類学的意義をもつものとは思われない. 一方 ,第1型と他の3っの型とははっきりと異なり,その中間的なものはほとんどみられない.第1型はウシノケグサ亜科のコムギ族,ヤマカモジグサ属スズメノチャヒキ属にみられるが,それらに近縁の植物,つまりカラスムギ族,Monermeae,ウシノケグサ族(スズメノチャヒキ亜族とヤマカモジグサ亜族をのぞく)では,すべて第4型がみられる.第1型と第4型とは,そのでんぷん粒の形成過程に相当の差異があるように思われ,この2つの型の間の差異は分類学的に意義のあるものである.古くから使われているような単粒と複粒にわける見方では,種子でんぷん粒をイネ科の系統分類に正しく使用することができないことは明らかである.(国立遺伝学研究所)