Seed coat morphology of Castilleja from Texas.
Castilleja Mutis ex L. f. (Scrophulariaceae) is a genus of more than 200 species centered in western North America. Nine species of Castilleja have been reported to occur in Texas (Correll and Johnston, 1970). Indian Paintbrush, as members of the genus commonly are termed, also occurs in other regions of the world, particularly Mexico and Central America. There are two species in eastern North America, about 15 species in South America, and five species have been reported from northern Asia (Cronquist et al., 1984).
Scanning Electron Microscope (SEM) studies of seed coat characteristics have been quiet useful in evaluating taxonomic relationships within the Scrophulariaceae. Data gathered from studies of seed coat morphology have provided important intrageneric information concerning sectional delimitations for several genera. Chuang and Heckard (1983) provided data of this type for Orthocarpus, supporting the sectional delimitation in that genus with minor revisions. Similar supporting data were provided in the genus Cordylanthus by Chuang and Heckard (1972). Data gathered from seed coat morphology of Castilleja may provide similar taxonomically valuable information. Seed coat differences in Castilleja have provided taxonomically significant data where similar species were compared to determine specific delimitations (Heckard et al. 1980). There are many other instances where seed coat characteristics have been utilized for taxonomic purposes in other genera of the Scrophulariaceae as well as other families (Wiffin and Tomb 1972; Canne 1979, 1980; Clark and Jernstedt 1979; Crow 1979; Elisens and Tomb 1983).
In this study, seeds from all nine species of Castilleja that occur in Texas were examined to determine if seed-coat characteristics could provide criteria useful for delimitating taxa at various levels. The nine species of Castilleja that occur in Texas are: C. ciliata Penn., C. elongata Penn., C. indivisa Engelm., C. integra Gray, C. lanata Gray, C. latebracteata Penn., C. purpurea (Nutt.) G. Don., C. sessiliflora Penn., and C. tortifolia Penn.
MATERIALS AND METHODS
Material was collected by the author and herbarium specimens were utilized from the Sul Ross State University Herbarium (SRSC). Dry mature seeds were removed from capsules of field collected material and herbarium sheets. Randomly chosen seeds were prepared for SEM study by placing them in Elmer's glue on an aluminum specimen stub that had been covered with 3M double-stick tape. The seeds then were sputter-coated with approximately 10 nm of gold-palladium using a Technics Hummer IV coater, and were then viewed and photomicrographed using a JEOL JSM-35C scanning electron microscope run at 10 and 15 kV. Using Polaroid Instant Film, type PN 55, photomicrographs were taken of typical seeds from each taxon at X60 and X360. Seeds of C. latebracteata were photomicrographed at X44 due to size. Several seeds were examined from each taxon.
Seeds examined were of a single basic type in that all had a loosely fitting outer testa with an embryo freely suspended within the testa. The seed coats are moderately or deeply reticulate with layers of scalariform thickenings on the radial walls. The number of layers ranges from two to 10 (Table 1). Each cell also contains a membrane that ruptures at maturity. Seeds vary in length from 1.2 to 3.2 mm. In shape, seeds are oblong to ovoid and are narrower at the micropylar end where the funiculus was terminally attached. Seeds of the nine species of Castilleja were divided into four morphological types based on the shape of the cells that make up the testa. The first group (type 1) contained five species, C. elongata, C. integra, C. purpurea, C. sessiliflora, and C. tortifolia. The second group (type 2) contained two species, C. ciliata and C. indivisa. The remaining two groups contained one species each, C. lanata (type 3) and C. latebracteata (type 4).
Type 1 seeds are characterized by large, regularly shaped cells. The cells are typically four sided and often square in all five species. Castilleja elongata exhibits two differently ornamented testa. In both seed types, cells are square and fairly regular in shape over the seed (Figs. 1, 3). Some seeds exhibit smooth tangential walls (Fig. 2) and others are covered with spinose protuberances (Fig. 4). In both seed types the radial walls are three layers thick. Seed size ranges from 1.5 to 2.6 mm in length. The seed coat of C. purpurea is characterized by regularly shaped cells with curved radial walls. The cells are large and regular in shape (Fig. 5). The radial walls are totally unornamented (Fig. 6) and are four layers thick. Seeds vary in from 1.4 to 2.0 mm in length. The seeds of C. integra are similar in appearance to those of C. elongata, having regularly shaped cells (Fig. 7). The testa walls of C. integra are densely covered with spinose protuberances (Fig. 8), and are very similar to the highly ornamented form of C. elongata. Seeds of C. integra have nine layers of scalariform thickenings in the radial walls as compared to three in C. elongata. Seed size ranges from 1.0 to 2.0 mm in length. The seeds of C. tortifolia, have the same regularly shaped cells as the previous three (Fig. 9). The radial walls are highly ornamented and seven layers thick (Fig. 10). The seeds of C. tortifolia are the smallest of the species covered here, ranging in length between 0.8 and 1.5 mm. The seeds of C. sessiliflora have regularly shaped cells (Fig. 11) with unornamented cell walls (Fig. 12). In addition, the cell walls are only two layers high. The seeds range from 1.6 to 2.3 mm in length.
[FIGURES 1-4 OMITTED]
[FIGURES 5-8 OMITTED]
Type 2 seeds are characterized by irregularly shaped cells. The cells are typically three to four times longer than wide. The testa of C. ciliata is composed of large, elongate cells (Fig. 13). The cell walls are densely ornamented with short, rounded protuberances (Fig. 14). Total seed length ranges from 1.2 to 2.0 mm. The other species in this group, C. indivisa, has more elongate cells (Fig. 15). The radial walls are unornamented and narrow compared to the previous taxa (Fig. 16). The seeds of C. indivisa vary in length from 1.2 to 1.8 mm.
Type 3 seed coat is chracterized by a very thick testa. Castilleja lanata exhibits this type of seed coat (Fig. 17). Each cell has eight to 10 layers of scalariform thickenings, this character gives the seed a deep honeycomb appearance. The radial walls are unornamented and narrow (Fig. 18). Seeds vary in length between 1.3 and 1.9 mm.
Type 4 seed coat has extremely elongate cells and a very thin testa. In the testa of C. latebracteata, the cells are many times longer than wide (Fig. 19). The radial walls of these cells are weakly ornamented with rounded projections (Fig. 20). The length of the seeds vary from 1.9 to 2.8 mm.
The external morphologies of the seed coats of the various taxa as revealed through the SEM provide many taxonomically useful characters. Each species considered here can be identified using seed coat characters. The combination of the size and shape of cells that make up the testa, the ornamentation of the radial walls of those cells, and the number of scalariform thickenings in the testa allow for precise identification at the species level. The number of scalariform thickenings, in addition to being a taxonomic character, also gives a quantitative measure to thickness of the testa. With the exception of C. elongata all species examined appear to be monomorphic in seed coat ornamentation in Texas.
The nine species described here all are closely related as they share the same basic seed coat pattern. The existence of different seed forms, other than the various structural differences discussed here, has not been discovered. Closely related species in other Scrophulariaceae genera have been proven to have the same basic seed coat patterns and more distantly related species may have different seed forms (Chuang and Heckard, 1972, 1983; Canne, 1979, 1980). These same studies revealed that the same general seed coat forms are seen in several genera, including the general seed coat form seen in Castilleja.
[FIGURES 9-12 OMITTED]
The seed coat data provided by this investigation are too limited to make any intrageneric evaluations. However, if the seed coat morphologies of Castilleja are examined on a large scale, such delimitations may be possible.
[FIGURES 13-16 OMITTED]
[FIGURES 17-20 OMITTED]
Vouchers at SRSC.
Castilleja ciliata Penn. -- TEXAS: Jeff Davis Co., Lockwood 188, Warnock 7460.
C. elongata Penn. -- TEXAS: Brewster Co., Lockwood 183.
C. indivisa Engelm. -- TEXAS: Bell Co., Marak 18.
C. integra Gray -- TEXAS: Brewster Co., Lockwood 138, 203; Jeff Davis Co., Lockwood 202, 203.
C. lanata Gray -- TEXAS: Brewster Co., Lockwood 134, 224.
C. latebracteata Penn. -- TEXAS: Brewster Co., Lockwood 108; Presidio Co. Hughes 4.
C. purpurea (Nutt.) G. Don. -- TEXAS: Coleman Co., Tharp s.n.; Crockett Co., Read 141.
C. sessiliflora Penn. -- TEXAS: El Paso Co., Warnock 10392; Terrell Co., Surratt 185; Val Verde Co., Warnock 11318.
C. tortifolia Penn. -- TEXAS: Brewster Co., Lockwood 204, 205, 226.
TABLE 1. Seed coat morphology comparison of nine Castilleja species from Texas. C. ciliata C. elongata C. indivisa Cell shape: regular - + - Radial walls: ornamented + +,- - width 25 [micro]m 20 [micro]m 10 [micro]m Thickness of testa (1) 2 3 2 Mean seed length 1.8 mm 2.1 mm 1.5 mm C. integra C. lanata C. latebracteata Cell shape: regular + + - Radial walls: ornamented + - - width 30 [micro]m 10 [micro]m 25 [micro]m Thickness of testa (1) 9 10 (2) 2 Mean seed length 1.7 mm 1.6 mm 2.6 mm C. purpurea C. sessiliflora C. tortifolia Cell shape: regular + + + Radial walls: ornamented - - + width 15 [micro]m 35 [micro]m 35 [micro]m Thickness of testa (1) 4 2 7 Mean seed length 1.7 mm 2.0 mm 1.2 mm (1) Number of scalariform thickenings present in outer testa. (2) Distance between layers of scalariform thickenings is greater in C. lanata than in other species.
I would like to thank Dr. Jim Richerson for suggestions on a previous draft and the curator of SRSC, Dr. Michael Powell, for the use of the Castilleja specimens.
Canne, J. M. 1979. A light and scanning electron microscope study of seed morphology in Agalinis (Scrophulariaceae) and its taxonomic significance. Syst. Bot., 4:281-296.
______. 1980. Seed surface features in Aureolaria, Brachystigma, Tomanthera, and certain South American Agalinis (Scrophulariaceae). Syst. Bot., 5:241-252.
Chuang, T. I., and L. R. Heckard. 1972. Seed-coat morphology in Cordylanthus (Scrophulariaceae) and its taxonomic significance. Amer. J. Bot., 59:258-265.
______. 1983. Systematic significance of seed-surface features in Orthocarpus (Scrophulariaceaesubtribe Castillejinae). Amer. J. Bot., 70:877-890.
Clark, C., and J. A. Jernstedt. 1979. Systematic studies of Eschsholizia (Papaveraceae) II. Seed coat microsculpturing. Syst. Bot., 3:386-402.
Correll, D. S., and M. C. Johnston. 1970. Manual of the vascular plants of Texas. Texas Research Foundation, Renner, Texas, xv + 1881 pp.
Cronquist, A., A. Holmgren, N. H. Holmgren, J. Reveal, and P. Holmgren. 1984. Intermountain flora: vascular plants of the intermountain west, USA, vol. 4, New York Bot. Garden, 573 pp.
Crow, G. E. 1979. The systematic significance of seed morphology in Sagina (Caryophyllaceae) under scanning electron microscopy. Brittonia, 31:52-63.
Elisens, W. J., and A. S. Tomb. 1983. Seed morphology in new world Antirrhineae (Scrophulariaceae): systematic and phylogenetic implications. Plant Syst. Evol., 142:23-47.
Heckard, L. R., M. I. Morris, and T. I. Chuang. 1980. Origin and taxonomy of Castilleja montigena (Scrophulariaceae). Syst. Bot., 5:71-85.
Wiffin, T., and A. S. Tomb. 1972. The systematic significance of seed morphology in the neotropical capsular fruited Melastomataceae. Amer. J. Bot., 59:411-422.
Department of Biology, Sul Ross State University, Alpine, Texas 79832.
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|Publication:||The Texas Journal of Science|
|Date:||May 1, 1992|
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