The taxonomic value of leaf anatomy for species Byrsonima: a difficult genus of Malpighiaceae Juss.

ABSTRACT

We studied the leaf anatomy of 15 species of Byrsonima and a single species of Diacidia as an outgroup to test the relevance of leaf anatomical characters to the complicated taxonomy of this genus. We present complete anatomical descriptions for petioles and leaf blades, together with an anatomical matrix, dendrogram and an identification key for the studied taxa. The most informative characters were the presence of stomatal crest, trichome type, epidermis type, contour and conformation of the vascular system in the diaphragm and medium petiole and number of accessory bundles. The aforementioned characters revealed that the anatomy of the petioles in the genus differs from that of petioles in the outgroup taxon with regard to vascular system conformation and the absence of cortical sclereids. Furthermore, the anatomy of the leaf blade appears to be quite informative in Byrsonima, especially in synonymized species. The anatomical features evaluated here have great value for Byrsonima taxonomy. These features may be used in an evolutionary approach to the group, especially for proposing a new classification system based on morphoanatomical characters of the genus.

Keywords:
murici; plant anatomy; similarity analysis; taxonomy

Introduction

Malpighiaceae is a pantropical plant family comprising 75 genera and ca. 1300 species, with most of them (75 %) being endemic to the Neotropics, especially in the Brazilian territory where 45 genera and 530 species occur (Davis & Anderson 2010; BFG 2018; Almeida et al. 2016). Byrsonima is the second largest genus of the family with ca. 135 tree and shrub species (Anderson et al. 2006; Almeida et al. 2016) and is phylogenetically related to Blepharandra and Diacidia (Davis & Anderson 2010). The species of Byrsonima are popularly known as murici in Brazil, and as nanche in the remaining Latin-America countries, where its fruits are largely consumed in natura by human populations (Anderson et al. 2006).

Byrsonima was divided into two subgenera, Byrsonima and Macrozeuma, based on the connectors morphology (equal in height to the locules or more) and the color of the anthesis petals (yellow or white / pink, respectively) (Niedenzu 1901; 1928). The first taxonomic revisions of Byrsonima were published in the early twentieth century by Niedenzu (1897; 1901), alongside with an infrageneric classification with several sections and subsections based exclusively on leaf features. However, the new molecular phylogeny for Byrsonima point out the polyphyletism of the subgenera Byrsonima and Macrozeugma (Davis & Anderson 2010) and evidences the absence of a classification system that reflects the evolutionary history of the genus Byrsonima.

Although being taxonomically complicated, the genus Byrsonima can be recognized by its terminal inflorescences, elongated thyrses with 1-3-flowered cincinni; cucullate lateral petals and fleshy drupaceous fruits (Fig. 1) (Anderson et al. 2006; Almeida et al. 2016). However, Byrsonima does not have the characteristic leaf glands of Malpighiaceae, making it difficult to distinguish species in absence of fertile material (Anderson 1981).

Figure 1
Petiole anatomy in Byrsonima and Diacidia. Species A. biconvex petiole contour in Byrsonima cydoniifolia. B. biconvex petiole contour with two lateral protuberances in B. spicata. C. plane-convex petiole contour in Diacidia aracaensis. D. circular petiole contour in B. crispa. E. plane-convex petiole contour in B. gardneriana. F. details of accessory bundles (black arrow) of petioles in B. cydoniifolia. G. collateral vascular bundle in D. aracaensis. Abbreviations: P= phloem; X= xylem; S= sclerenchyma.

Therefore, anatomical data may be relevant for a taxonomic approach in the group, considering plant anatomy has been historically used as an important tool in the biological classification of plants. It provides additional informative features which helps to understand its morphological evolution (Metcalfe & Chalk 1979; Endress et al. 2000). Leaf anatomy is widely used as an aid in flowering plants taxonomy, especially in groups with taxonomic problems, as in Malpighiaceae (Metcalfe & Chalk 1957; Gomes et al. 2009; Araújo et al. 2010; Almeida-Jr et al. 2013; Almeida et al. 2017; Guesdon et al. 2018; Almeida et al. 2019; Araújo et al. 2020). Even though leaf anatomy of Byrsonima species has been explored in previous studies, few have listed features that can be attributed to a new classification system for the genus (Araújo et al. 2010; Silva 2014).

We present the anatomical study of leaves from 15 species of Byrsonima, including representatives of the two subgenera according to Niedenzu (1901; 1928), in order to test the taxonomic relevance of leaf anatomy in the group. Diacidia aracaensis was also included to provide a comparative standard. In addition, we provide a matrix with the relevant anatomical data for future studies and a dendrogram obtained from the morphological matrix.

Materials and methods

The selected species of Byrsonima represent distinct infrageneric categories established in classic taxonomical studies (Niedenzu 1901; 1928) described in Table 1. Diacidia aracaensis was selected as an outgroup due to its phylogenetic proximity to Byrsonima (Davis & Anderson 2010). Byrsonima correifolia, B. gardneriana and B. sericea fully expanded leaves (collected in Pai Cormo village, Pedro II city, Piaui state, Brazil; São Brás village, Pedro II city, Piauí state, Brazil; Lagoa do Boi village, Pastos Bons city, Maranhão state, Brazil, respectively) were fixed in the field using FAA (formaldehyde, acetic acid and 50 % etanol; 1:1:18 by volume) (Johansen 1940) and the control material was deposited in a herbarium (HAF / UESPI).The remaining species were taken from herborized material from different herbariums, as shown in Table 1. Herborized leaves were boiled in distilled water until full submersion for a maximum of 10 minutes, kept in a 2 % potassium hydroxide solution for two hours in room temperature, washed in distilled water several times, dehydrated in an ethanol series, and kept in 70 % ethanol (Smith & Smith 1942). Byrsonima cydoniifolia A.Juss. and B. orbignyana A.Juss. are currently synonyms (Anderson et al. 2006), but were separately analyzed, since we recognized distinct patterns on their leaf anatomy. All specimens were manually sectioned using a razor blade on the middle third of petioles, midrib, and semi limb, followed by immersion in 50 % sodium hypochlorite, and staining in basic fuchsin and Astra blue (Roeser 1972). Epidermal dissociations were obtained from leaf fragments immersed in chromic and nitric acids solution 1:1 (v/v) for 24 hours to dissociate the epidermis (Johansen 1940). Temporary slides were mounted in 50 % glycerin and sealed with colorless varnish.

Table 1
List of species and vouchers used in this study.

Subgenera (Niedenzu 1901; 1928)	Sections (Niedenzu 1901; 1928)	Species	Collector / number or Accession number
Byrsonima	Eriolepsis	Byrsonima crassifolia (L.) Kunth	TEPB25696; TEPB26727; TEPB14611
		Byrsonima cydoniifolia A.Juss.	A. Francener 1246 (SP); TEPB32026; TEPB32019
		Byrsonima guilleminiana A. Juss.	A. Francener 1240 (SP); 1129 (SP)
		Byrsonima orbignyana A. Juss.	HAF2731
		Byrsonima pachyphylla A.Juss.	R.F. Almeida 730 (HUEFS), A. Francener 1147 (SP)
		Byrsonima verbascifolia (L.) DC.	TEPB547, TEPB6073, TEPB5642
	Sericolepsis	Byrsonima chrysophylla Kunth	A. Francener 1324 (SP); A. Francener 1231 (SP); A. Francener 1346 (SP)
		Byrsonima crispa A.Juss.	A. Francener 1329 (SP)
		Byrsonima intermedia A.Juss.	HAF03460; HAF03235; HAF03457
		Byrsonima laxiflora Griseb.	A. Francener 1186 (SP); 1201 (SP)
		Byrsonima sericea DC.	TEPB14609, TEPB17024, TEPB3652, HAF04357, HAF04407
		Byrsonima spicata Rich. ex Kunth	T.A.P. Santos 19 (MFS)
Macrozeugma	Colobotheca	Byrsonima correifolia A.Juss.	HAF03545; HAF03546; HAF03547; TEPB17115; TEPB27035; TEPB22793
		Byrsonima gardneriana A.Juss.	TEPB20333; HAF745; HAF2727
		Byrsonima ligustrifolia A.Juss.	TEPB26729, TEPB26730
Outgroup	______	Diacidia aracaensis W.R.Anderson	G.T. Prance 29105 (US)

Photograph records were taken using a Nikon® E100 photomicroscope, projecting the micrometric scale on the same optical conditions. The classification of vascular bundles contour follows Howard (1979), trichome classification follows Theobald et al. (1979), and Metcalfe & Chalk (1979), and stomata classification also follow Metcalfe & Chalk (1979).

All the Byrsonima species and Diacidia aracaensis were compared according to their analyzed structural characteristics using a presence/absence matrix (Tab. 2). This matrix used Jaccard’s index and an average group linkage technique (also known as unweighted pair-group method using arithmetic averages, UPGMA) with software Past 3.19 (Hammer et al. 2001). The definition of the maximum similarity values was made using the software RANDMAT 1.0. A total of two thousand replications were used (a = 1 %).

Table 2
Morphological matrix of binary characters (absence/presence) including 15 species of Byrsonima and its outgroup. 1. Non-continuous bistratified epidermis on the adaxial surface, 2. Non-continuous biestratified epidermis on the abaxial surface, 3. Unistratified epidermis on both sides, 4. Laterocytic paracytic stomata, 5. Paracytic stomata, 6. Stomatal crests, 7. V-shaped trichomes, 8. Y-shaped trichomes, 9. T-shaped trichomes, 10. Dorsiventral mesophyll, 11. Isobilateral mesophyll, 12. Extension of the parenchymal sheath in the bundles in the mesophyll, 13. Extension of the sclerified sheath in the bundles in the mesophyll, 14. Plane-convex midrib in cross-section, 15. Biconvex midrib in cross-section, 16. Midrib with biconvex vascular system, 17. Midrib with plane-convex vascular system, 18. Midrib with concave-convex vascular system, 19. Midrib with vascular system with 3-4 dorsal bundles and an open arch, 20. Midrib with phloem in the medullary region, 21. Plane-convex petiole in cross-section, 22. Biconvex petiole in cross-section, 23. Circular petiole in cross-section, 24. Petiole with two lateral protuberances in cross-section, 25. Petiolar vascular system arranged in an arc with convoluted extremities, 26. Vascular system consisting of bundles arranged in an arch and several medullary bundles, 27. One pair of accessory bundles in the petiole, 28. More than a one pair of accessory bundles in the petiole, 29. Petiole with phloem in the medullary region, 30. Dispersed sclereids in the cortical region in the petiole, Abbreviations: Byrsonima correifolia - Bcor; B. crassifolia - Bcra; B. crispa - Bcri; B. chrysophyla - Bchr; B. cydoniifolia- Bcyd; B. gardneriana - Bgar; B. guilleminiana- Bgui; B. intermedia - Bint; B. laxiflora- Blax; B. ligustrifolia - Blig; B. orbigyniana - Borb; B. pachyphylla- Bpac; B. sericea - Bser; B. spicata- Bspi; B. verbascifolia - Bver e Diacidia aracaensis- Dara.

	1	2	3	4	5	6	7	8	9	10	11	12	13	14	15	16	17	18	19	20	21	22	23	24	25	26	27	28	29	30
Bcor	0	0	1	1	0	0	1	1	1	0	1	0	1	1	0	1	0	0	0	0	1	0	0	0	1	0	1	0	0	1
Bcra	1	0	0	1	0	1	0	0	1	0	1	0	1	0	1	1	0	0	0	1	0	1	0	0	1	0	1	0	1	1
Bcri	0	0	1	1	0	1	0	0	0	1	0	1	0	0	1	1	0	0	0	1	0	0	1	0	1	0	0	1	0	1
Bcrh	1	0	0	1	0	0	0	0	1	0	1	1	0	0	1	1	0	0	0	1	0	1	0	1	1	0	0	1	0	1
Bcyd	1	0	0	0	1	0	0	0	1	0	1	0	1	0	1	1	0	0	0	1	0	1	0	0	1	0	0	1	1	1
Bgar	0	0	1	0	1	0	0	0	0	0	1	1	0	0	1	0	0	0	1	0	1	0	0	0	1	0	1	0	0	1
Bgui	1	0	0	1	0	1	0	0	1	0	1	0	1	0	1	1	0	0	0	1	1	0	0	0	1	0	1	0	0	1
Bint	1	1	0	0	1	1	0	0	1	0	1	0	1	1	0	1	0	0	0	1	0	1	0	0	1	0	0	1	1	1
Blax	1	0	0	1	0	1	0	0	1	0	1	0	1	0	1	1	0	0	0	1	1	0	0	0	1	0	0	1	0	1
Blig	1	0	0	0	1	0	0	0	0	1	0	1	0	0	1	0	0	1	0	0	0	1	0	0	1	0	1	0	0	1
Borb	0	0	1	0	1	0	0	0	1	0	1	1	0	0	1	0	1	0	0	1	0	1	0	0	1	0	0	1	1	1
Bpac	1	0	0	1	0	0	0	0	1	0	1	1	0	0	1	1	0	0	0	1	1	0	0	0	1	0	0	1	0	1
Bser	1	0	0	1	0	1	0	0	1	0	1	0	1	0	1	1	0	0	0	1	0	1	0	0	1	0	0	1	0	1
Bspi	0	0	1	1	0	1	0	0	1	0	1	1	0	0	1	1	0	0	0	1	0	1	0	1	1	0	0	1	0	1
Bver	1	0	0	0	1	1	0	0	1	0	1	0	1	0	1	0	1	0	0	1	0	1	0	0	1	0	1	0	0	1
Dara	1	0	0	0	1	0	0	0	1	1	0	1	0	1	0	0	0	0	1	0	1	0	0	0	0	1	1	0	0	0

Results

The petiole contour is biconvex in Byrsonima ligustrifolia, B. intermedia, B. cydoniifolia (Fig. 1A), B. crassifolia, B. orbignyana, B. sericea, B. verbascifolia; petioles with two adaxial protuberances in B. chrysophylla and B. spicata (Fig. 1B); contour plane-convex in B. correifolia, B. gardneriana, B. guilleminiana, B. laxiflora, B. pachyphylla and D. aracaensis (Fig. 1C); and circular contour in B. crispa (Fig. 1D). The main vascular system of petioles is collateral in all species of Byrsonima and the conformation of bundles is an open arch with convoluted extremities (Fig. 1A, B, E), followed by a pair of accessory bundles and the occurrence of dispersed druses and sclereids in the cortical region in most species (Fig. 1D). There are more than one pair of accessory bundles in B. crispa, B. chrysophylla, B. cydoniifolia, B. intermedia, B. laxiflora B. pachyphylla, B. sericea and B. spicata (Fig. 1F). The occurrence of medullary phloem in petioles was exclusive from B. crassifolia, B. chrysophylla, B. cydoniifolia (Fig. 1A) and B. intermedia. In Diacidia aracaensis, the vascular system consists of bundles arranged in an arch and several medullary bundles (Fig. 1C), all collateral (Fig. 1G).

The midribs contour is plane-convex in B. correifolia (Fig. 2A), B. intermedia and D. aracaensis, and biconvex in the remaining species (Fig. 2B, C). In all species bundles are collateral (Fig. 2A), but the vascular system conformation varies, being biconvex in two open arches surrounded by fibers with no medullary phloem in B. correifolia (Fig. 2A); concave-convex in two arches interleaved by sclerenchyma in B. ligustrifolia (Fig. 2B); biconvex in two arches surrounded by fibers and interrupted by medullary phloem in Byrsonima crassifolia, B. crispa, B. chrysophylla, B. cydoniifolia, B. guilleminiana, B. intermedia, B. laxiflora, B. pachyphylla, B. sericea e B. spicata (Fig. 2C); collateral bundles adjacently aligned to the adaxial surface and in an arch facing the adaxial surface in D. aracaensis (Fig. 2D); three to four dorsal bundles and an open arch in B. gardneriana (Fig. 2E); and plane-convex in two arches surrounded by fibers and medullary phloem in B. verbascifolia (Fig. 2F) and B. orbignyana. In Diacidia aracaensis, the vascular system consists of bundles arranged in an arch and three dorsal bundles, all surrounded by fibers (Fig. 2D).

Figure 2
Midrib anatomy in Byrsonima and Diacidia species A. plane-convex midrib contour and biconvex vascular system with no phloem in B. correifolia. B. biconvex midrib contour and concave-convex vascular system in B. ligustrifolia. C. biconvex vascular system with medullar phloem B. chrysophylla midrib. D. midrib vascular system in Diacidia aracaensis. E. vascular system in open arch and three bundles in B. gardneriana midrib. F. plane-convex vascular system with medullar phloem in of B. verbascifolia midrib. Abbreviations: P= phloem; X= xylem; S= sclerenchyma.

Leaves are hypostomatic with adaxial cells larger in dimension than those from the abaxial surface (Fig. 3A). The epidermis is unistratified in B. correifolia, B. crispa, B. gardneriana (Fig. 3A), B. spicata and B. orbignyana and the adaxial surface of the epidermis is bistratified non-continuous in most species, as B. ligustrifolia (Fig. 3B), except for Byrsonima intermedia which was the only species with bistratified non-continuous epidermis on both surfaces (Fig. 3C). Paracytic stomata are predominant in all species, and laterocytic paracytic stomata were observed in Byrsonima correifolia, B. crispa, B. chrysophylla, B. crassifolia, B. guilleminiana, B. laxiflora, B. pachyphylla, B. sericea and B. spicata (Fig. 3D). Stomatal crests are also found in B. crassifolia, B. crispa (Fig. 3E), B. intermedia, B. guilleminiana, B. laxiflora, B. sericea, B. spicata and B. verbascifolia; while not observed in other species. Trichome scars are observed in Byrsonima crassifolia, B. crispa, B. chrysophylla, B. cydoniifolia, B. gardneriana, B. guilleminiana, B. intermedia, B. ligustrifolia (Fig. 3F), and B. sericea. No trichomes were found in Byrsonima crispa and B. ligustrifolia (Fig. 3F), only trichome scars. Y-T-V-shaped trichomes, with peduncles varying in size, were recorded in B. correifolia (Fig. 3G, H, I). T-shaped trichomes were recorded in B. crassifolia (Fig. 3I), B. chrysophylla, B. cydoniifolia, B. guilleminiana, B. laxiflora, B. orbignyana, B. pachyphylla, B. sericea, B. spicata, B. verbascifolia, B. intermedia and Diacidia aracaensis.

Figure 3
Leaf blade anatomy of Byrsonima and Diacidia. A. Isobilateral mesophyll with unistratified epidermis and stomata (black arrow) on the abaxial surface of B. gardneriana. B. Dorsiventral mesophyll with bistratified epidermis of B. ligustrifolia. C. B. intermedia mesophyll showing the bistratified non continuous epidermis on both surfaces of the leaf blade. D. paracytic and paracytic laterocytic stomata in B. spicata. E. stomatal crests in B. spicata. F. hair scar in B. ligustrifolia. G. Y-shaped hair in B. correifolia. H. V-shaped hair in B. correifolia. I. T-shaped hair of B. crassifolia. J. B. ligustrifolia parenchymal extension (black arrow) and vascular bundles sheath K. Sclerified leaf sheath extension (black arrow) of the vascular bundle in B. correifolia mesophyll. Abbreviation: SC= subsidiary cells.

Two types of mesophyll were observed in the studied species: isobilateral in most species, such as Byrsonima gardneriana (Fig. 3A) and dorsiventral mesophyll in B. crispa, B. ligustrifolia (Fig. 3B) and D. aracaensis. Vascular bundles in the mesophyll are collateral and circled by a parenchymal sheath in all species, while larger bundles show the same sheath extension in B. crispa, B. chrysophylla, B. gardneriana, B. ligustrifolia, B. pachyphylla, B. spicata and D. aracaensis (Fig. 3J). In the remaining species, the sheath extension occurs facing the adaxial surface and is sclerified (Fig. 3K).

Based on the anatomical diversity, petiole and midrib features were used to elaborate an identification key for the studied species, presented below.

Identification key for the studied species of Byrsonima and Diacidia

1. Vascular system with sclereids dispersed in the petioles….………….………………….… 2

1’. Vascular system with no sclereids dispersed in the petiole..….…..…... Diacidia aracaensis

2. Petiole with circular contour………………………………………………. Byrsonima crispa

2’. Petiole with plane-convex to biconvex contours……………………..….………………… 3

3. Petiole with plane-convex contour…………………………………………..……………... 4

3’. Petiole with biconvex contour………………………………………………..……………. 8

4. Vascular system of the midrib with three or four dorsal bundles and with an open arch..……………………………………..……………...…………… Byrsonima gardneriana

4’. Vascular system of the midrib with no dorsal bundles and no open arch facing the same surface………………………………………...……………………………..……….….……. 5

5. Vascular system of the midrib biconvex with two arches and no medullar phloem…………………………………………..……………………... Byrsonima correifolia

5’. Vascular system of the midrib biconvex with two arches and with medullary phloem....... 6

6. One pair of accessory bundles associated to the vascular system of petioles……………………………….……………………………... Byrsonima guilleminiana

6’. More than one pair of accessory bundles associated to the vascular system of petioles……………………………………………………………………………..…………. 7

7. Presence of stomatal crests on the leaves………………………….…… Byrsonima laxiflora

7’. Absence of stomatal crests on the leaves.………………………….. Byrsonima pachyphylla

8. Presence of two lateral protuberances in the petiole contour……………….…………….... 9

8’. Absence of two lateral protuberances in the petiole contour……………….……………. 10

9. Presence of stomatal crests on the leaves…………………………….…... Byrsonima spicata

9’. Absence of stomatal crests on the leaves.……………………….… Byrsonima chrysophylla

10. Presence of phloem in the medullary region of petioles………………….………………. 11

10’. Absence of phloem in the medullary region of petioles……………….………………… 14

11. One pair of accessory bundles associated to the vascular system of petioles………………………………………………………………...... Byrsonima crassifolia

11’. More than one pair of accessory bundles associated to the vascular system of petioles………………………………………………………………………………………. 12

12. Unistratified epidermis…………………………………………… Byrsonima orbignyana

12’. Bistratified epidermis……………………………………………………………….….. 13

13. Non-continuous epidermis only on the adaxial surface…………… Byrsonima cydoniifolia

13’. Non-continuous epidermis on both surfaces……………………… Byrsonima intermedia

14. Vascular system of the midrib biconvex with two arches with medullary phloem…………………………………………………………..…………. Byrsonima sericea

14’. Vascular system of the midrib plane-convex or concave-convex……………………… 15

15. Vascular system of the midrib plane-convex with two arches with medullary phloem…………………………………………………………..…… Byrsonima verbascifolia

15’. Vascular system of the midrib concave-convex…….…………… Byrsonima ligustrifolia

Similarity analysis

A similarity analysis with UPGMA (Fig. 4) organizes all the evaluated species of Byrsonima in a group different from Diacidia aracaensis. This difference is attributed to the absence of sclereids dispersed in the cortical region of the petiole in Diacidia aracaensis in the vascular system present in the outgroup. Furthermore, the group formed by Byrsonima species is consistent in the analysis and point only Byrsonima correifolia, B. gardneriana and B. ligustrifolia for less similarity than the other species, especially because they do not present phloem in the medullary region of the median vein. The highest degree of similarity appears between B. laxiflora, B. sericea and B. guilleminiana (group 1) due to the similarity of the epidermis, especially due to the presence of stomatal crests and trichomes only in T and also the extension of the sclerified sheath of the bundles in the mesophyll; the second group shows the high similarity of B. chrysophylla and B. spicata (group 2), due to the presence of parenchymal extension of the bundles in the mesophyll and the exclusive presence of petiole with two lateral protuberances in its contour.

Figure 4
Cluster analysis (UPGMA) of Byrsonima species. Abbreviations: Byrsonima correifolia - Bcor; B. crassifolia - Bcra; B. crispa - Bcri; B. chrysophyla - Bchr; B. cydoniifolia- Bcyd; B. gardneriana - Bgar; B. guilleminiana- Bgui; B. intermedia - Bint; B. laxiflora- Blax; B. ligustrifolia - Blig; B. orbigyniana - Borb; B. pachyphylla- Pac; B. sericea - Bser; B. spicata- Bspi; B. verbascifolia - Bver e Diacidia aracaensis- Dara.

Discussion

In the last sixty years, several studies were published on the morphological and classification aspects of Byrsonima, focusing on leaves indumentum, bracts and bracteoles, petal color, and anther shape (Niedenzu 1901; 1928). However, no authors explored the anatomy of vegetative organs as an aid to the taxonomy of the genus.

Based on leaf blade and petiole anatomical analyses, we have identified several informative characters that can be used to support a new classification in Byrsonima in future studies. The anatomy of petioles shows little influence of environmental pressure and might represent great taxonomic value in different taxa (Metcalfe & Chalk 1957). The four types of petiole contour found in our study corroborates the results presented by Silva et al. (2011), and studies on different genera, such as Stigmaphyllon (Guimarães et al. 2016), and Banisteriopsis (Araújo et al. 2020). The variation evidenced in this feature makes it a useful tool in the circumscription of species and genera in Malpighiaceae, especially in Byrsonima, the second largest and most taxonomic challenging genus in the family according to Almeida et al. (2016).

Petiole vascular system presents a similar conformation in all studied species of Byrsonima, except for Diacidia. Araújo et al. (2010) had already highlighted the similarity in conformation of bundles in species of Byrsonima, but the authors observed some variation on this structure within species of the genus. Studies exploring the conformation of vascular bundles in the petioles of Malpighiaceae are promising and may contribute with valuable taxonomic characters at the generic level (Araújo et al. 2010; Guimarães et al. 2016). In Byrsonima, the anatomy of petioles evidenced relevant data in the elaboration of an identification key and may subsidize future taxonomic and phylogenetic studies in the family. Nonetheless, it is important to highlight the need for standardization of the analyzed region in case of long petioles, since differences may occur. This fact would explain the data divergences in the conformation of the vascular system recorded in B. gardneriana and B. sericea in our study from the results obtained by Silva et al. (2011). The midrib contour showed variations already observed by previous authors in some species of Malpighiaceae, and in Byrsonima this variation was corroborated as important in the delimitation of species (Higuchi 2007; Araújo et al. 2010; Silva 2014). The presence of medullary phloem in the midrib is another distinctive character for Byrsonima and it has been used to differentiate genera and species in Malpighiaceae (Araújo et al. 2010; Silva 2014). The vascular system conformation in the midrib has also been regarded as an important feature by several authors due to the variation or constancy within species, representing a great phylogenetic signal in the genus (Araújo et al. 2010; Almeida et al. 2019; Mello et al. 2019; Araújo et al. 2020).

Paracytic stomata are widely distributed in Malpighiaceae (Metcalfe & Chalk 1957), and its occurrence in Byrsonima is corroborated by several authors (Higuchi 2007; Vasconcelos-Filho et al. 2008; Araújo et al. 2010; Silva 2014). On the other hand, the occurrence of other types of stomata is rare in the family, with only Ferreira et al. (2015) reporting anomocytic and tetracytic stomata in Byrsonima coccolobifolia. The presence of paracytic laterocytic stomata in Byrsonima evidenced in this study contributed to differentiate the analyzed species. Future studies sampling a larger dataset in the genus may evidence its relevance to the taxonomy of Byrsonima. Trichome scars were also observed in leaves of B. gardneriana by Silva et al. (2011), besides the presence of Y-T-shaped trichome in B. intermedia and T-shaped trichome in B. orbignyana. In anatomical and histochemical analysis made by Higuchi (2007) in leaves of Byrsonima species, the presence of long Y-shaped tector trichomes in B. basiloba and T-shaped in B. crassifolia was also reported. Additionally, the author did not observe tector trichomes in B. fagifolia and B. intermedia. However, young leaves of Byrsonima species analyzed by Attala (2004) showed trichomes in the adaxial surface, which probably provides protection during the process of leaf extension. Also, these same trichomes are later deciduous, leaving scars on mature leaves. For this reason, the lack of trichomes in B. ligustrifolia is justifiable, since trichome scars were only recorded on the leaf blades of expanded leaves.

Bistratified non-continuous epidermis on the adaxial surface was also observed by Araújo et al. (2010) in three from five analyzed species of Byrsonima, and by Silva et al. (2011) in two of three analyzed species of Byrsonima. On the other hand, all analyzed species by Higuchi (2007), Vasconcelos-Filho (2008) and Silva (2014) showed unistratified epidermis on both surfaces of the leaf blade. Bistratified epidermis was also found in Banisteriopsis and Heteropterys (Araújo et al. 2010), showing that this feature probably evolved multiple times independently in the family and it is an important character to differentiate species within genera in Malpighiaceae (Metcalfe & Chalk 1979). The type of mesophyll is widely used in identification keys elaborated from anatomical characters (Araújo et al. 2010; Silva 2014; Ferreira et al. 2015), and it has been an important aid to the taxonomy of Malpighiaceae. In relation to the bundles immersed in the mesophyll, the collateral type is characteristic of Malpighiaceae as described in several genera (Araújo et al. 2010; Silva 2014; Guimarães et al. 2016). The extension of the bundle sheath being sclerified or not has helped to distinguish species of Byrsonima, even though it has not been commonly described in anatomical studies of Malpighiaceae (Araújo et al. 2010).

Our findings are congruent with a recent anatomical study in Banisteriopsis, whose authors showed the taxonomic relevance of anatomical characters to support the monophyletism of informal groups, being promising in a new infrageneric classification (Araújo et al. 2020). In addition, characters such as biconvex contour of petioles with two protuberances, bistratified non-continuous epidermis on both surfaces of the leaf blade, paracytic laterocytic stomata, and medullary phloem in the petioles were reported here for the first time in Byrsonima and should be highlighted in future anatomical studies in Malpighiaceae.

The similarity analysis clearly distinguishes the Byrsonima species from its outgroup, and the anatomical data related to the vascular system justifies this distinction between the genera. Davis & Anderson (2010) recovered Byrsonima as a monophyletic group and the vascular system anatomy may contain potential synapomorphies in future studies based on molecular phylogeny. The most similar groups presented here include species placed in different infrageneric categories. These findings are consistent when the subgenera and their respective sections represent polyphyletic groups in Byrsonima, according to the molecular phylogeny by Davis & Anderson (2010). For instance, the species B. laxiflora, B. sericea (sect. Sericolepsis, subg. Byrsonima) and B. guilleminiana (sect. Eriolepsis, subg. Byrsonima) show great anatomical similarities and can be considered closely related in a future molecular analysis. Moreover, the analysis points out that Byrsonima orbignyana is distant from its synonym, B. cydoniifolia, due to anatomical differences as epidermis stratification, sheath extension of the mesophyll bundles and conformation of the midrib vascular system. Nonetheless, molecular studies using a greater sampling within the genus are needed in order to propose a new infragenetic classification and the anatomical characters described in this study may be a key element in the process.

Conclusions

In this study, we present the relevance of anatomical characters to Byrsonima taxonomy, especially in order to differentiate species and punctuate promising characters for a future infrageneric classification. Therefore, the following characters stand out taxonomically: stomatal crest, types of trichomes and epidermis, contour and conformation of the vascular system in the midrib and petiole, and number of accessory bundles. The petiole anatomy seems to be conserved in Byrsonima and midrib anatomy seems to be quite informative at species level. Several characters were first described in Byrsonima, such as bistratified epidermis on the adaxial surface of the leaves, laterocytic paracytic stomata and medullary phloem in the petioles. Furthermore, anatomical leaf studies are needed in order to establish a taxonomic circumscription of Byrsonima and closely related genera, as several differences have been recorded between Byrsonima and the outgroup (Diacidia aracaensis), and in the leaf anatomy of two species currently recognized as synonyms, B. cydoniifolia and B. orbignyana.

Acknowledgements

We would like to thank the curators and staff from all herbaria for their assistance, UESPI and Byrsonima do Piauí Project (EDITAL SECTEC-SEDET/UESPI 001/2016) for lab funding, CNPq Universal Project (Nº 422747/2016-5) for funding field and herbarium collections, and CAPES for partial funding (Finance Code 001). We are thankful for the availability of material from the PhD taxonomist Augusto Francener and to the revisors who evaluated our paper for their important contributions, in special to PhD Marcelo Pace.

References

• Almeida RF, Francener A, Amorim AMA. 2016. A generic synopsis of Malpighiaceae in the Atlantic Forest. Nordic Journal of Botany 34: 285-301.
• Almeida RF, Guesdon IR, Pace MR, Meira RMS. 2019. Taxonomic revision of Mcvaughia W.R.Anderson (Malpighiaceae): notes on vegetative and reproductive anatomy and the description of a new species. PhytoKeys 117: 45-72.
• Almeida RF, Mello ACMP, Oliveira DMT, Amorim AMA. 2017. Leaf anatomy and macro-morphology uncover a new species of Amorimia (Malpighiaceae) from Southeastern Brazil. Phytotaxa 305: 179-190.
• Almeida-Jr EB, Araújo JS, Santos-Filho FS, Zickel CS. 2013. Leaf morphology and anatomy of Manilkara Adans. (Sapotaceae) from northeastern Brazil. Plant Systematics and Evolution 299: 1-9.
• Anderson WR, Anderson CE, Davis CC. 2006. Malpighiaceae. Available at: Available at: http://herbarium.Isa.umich.edu/malpigh 5 Jun. 2019.
  » http://herbarium.Isa.umich.edu/malpigh
• Anderson WR. 1981. Malpighiaceae. In: The Botany of Guyana Highland - Part IX. Memoirs New York Botanical Garden 32: 21-305.
• Araújo JS, Almeida RFD, Meira RMSA. 2020. Taxonomic relevance of leaf anatomy in Banisteriopsis CB Rob. (Malpighiaceae). Acta Botanica Brasilica 34: 214-228.
• Araújo JS, Azevedo AA, Silva LC, Meira RMSA. 2010. Leaf anatomy as an additional taxonomy tool for 16 species of Malpighiaceae found in the Cerrado area (Brazil). Plant Systematics and Evolution 286:117-131.
• Attala NCA. 2004. Morfoanatomia da lâmina foliar, estrutura e histoquímica das glândulas foliares e calicinais em espécies de Malpighiaceae de cerrado. PhD Thesis. Universidade Estadual Paulista, São Paulo.
• BFG. 2018. Brazilian Flora 2020: Innovation and collaboration to meet Target 1 of the Global Strategy for Plant Conservation (GSPC). Rodriguésia 69: 1513-1527.
• Davis CC, Anderson WR. 2010. A complete generic phylogeny of Malpighiaceae inferred from nucleotide sequence data and morphology. American Journal of Botany 97: 2031-2048.
• Endress PK, Bass P, Gregory M. 2000. Systematic Plant Morphology and Anatomy: 50 years of Progress. Taxon 49: 401-434.
• Ferreira CS, Carmo WSD, Ribeiro DG, Oliveira JMFD, Melo RBD, Franco AC. 2015. Anatomia da lâmina foliar de onze espécies lenhosas dominantes nas savanas de Roraima. Acta Amazonica 45: 337-346.
• Gomes SM, Somavilla NSD, Gomes-Bezerra KM, Miranda SC, De-Carvalho PS, Graciano-Ribeiro D. 2009. Anatomia foliar de espécies de Myrtaceae: contribuições à taxonomia e filogenia. Acta Botanica Brasilica 23: 233-238.
• Guesdon IR, Amorim AMA, Meira RMSA. 2018. The hydrochorous Amazonian genus Glandonia (Malpighiaceae): new records, morphoanatomy updates, and taxonomic contributions. Phytotaxa 345: 13-25.
• Guimarães ALA, Costa RPC, Cabral LM, Vieira ACM. 2016. Comparative anatomy and chemical analysis of the vegetative organs of three species of Stigmaphyllon (Malpighiaceae). Flora 224: 30-41.
• Hammer O, Harper DAT, Ryan PD. 2001. PAST: Paleontological Statistics software package for education and data analysis. Palaeontologia Electronica 4: 9p. https://paleo.carleton.ca/2001_1/past/past.pdf
  » https://paleo.carleton.ca/2001_1/past/past.pdf
• Higuchi CT. 2007. Byrsonima spp: estudo anatômico e histoquímico foliar, atividade antimicobacteriana e citotoxicidade de extratos e seus derivados. MSc Thesis, Universidade Estadual Paulista, Araraquara.
• Howard RA. 1979. The petiole. In: MetCalfe CR, Chalk L. (eds.) Anatomy of the Dicotyledons. Systematic Anatomy of the leaf and stem. Oxford, Clarendon Press. p. 88-96.
• Johansen D. 1940. Plant Microtechnique. New York, McGraw Hill Book Company.
• Mello ACMP, Almeida RF, Amorim AMA, Oliveira DMT. 2019. Leaf structure in Amorimia and closely related Neotropical genera and implications for their systematics and leaf evolution in Malpighiaceae. Botanical Journal of the Linnean Society 190:1-26.
• Metcalfe CR, Chalk L. 1957. Anatomy of the Dicotyledons. Vol. I. Oxford, Clarendon Press .
• Metcalfe CR, Chalk L. 1979. Anatomy of the Dicotyledons . Vol. II. Oxford, Clarendon Press .
• Niedenzu F. 1897. De genere Byrsonima Brunsbergae, Typis Heynenis (G. Riebensahm).
• Niedenzu F. 1901. De genere Byrsonima (pars posterior). Vol. I. Brunsbergae, Typis Heynenis (G. Riebensahm) .
• Niedenzu F. 1928. Malpighiaceae. In: Engler A. (ed.) Das Pflanzenreich IV 141: 1-870.
• Roeser KR. 1972. Die nadel der schwarzkiefer-massenprodukt und kunstwerk der natur. Mikrokosmos 61: 33-36.
• Silva LNNS, Costa JMFP, Filho FSS, Araújo JS. 2011. Aspectos da Anatomia Foliar de três espécies de Byrsonima Rich. ex. Kunth. (Malpighiaceae) ocorrentes nas restingas do Piauí (Nordeste, Brasil) In: Santos-Filho FS, Soares AFCL, Almeida-Jr EB. (eds.) Biodiversidade do Piauí: pesquisas e perspectivas. Curitiba, Editora CRV. p. 191-199.
• Silva LNNS. 2014. Aspectos da anatomia foliar de espécies de Byrsonima Rich ex Kunth (Malpighiaceae) ocorrentes em diferentes tipos de vegetação no Estado da Bahia. MSc Thesis, Universidade Estadual de Santa Cruz, Ilhéus.
• Smith FH, Smith EC. 1942. Anatomy of the inferior ovary of Darbya American Journal of Botany 29: 464-471.
• Theobald WL, Krahulik JL, Rollins RC. 1979. Trichome description, and classification. In: Metcalfe CR, Chalk L. (eds.) Anatomy of the Dicotyledons .Vol. I. Systematic anatomy of the leaf and stem. 2nd. edn. Oxford, Oxford Claredon Press. p. 40-53.
• Vasconcelos-Filho SC. 2008. Caracterização anatômica e histoquímica de folhas, calogênese e fitoquímica de calos de murici (Byrsonima verbascifolia Rich. ex A.Juss.). PhD Thesis, Universidade Federal de Viçosa, Minas Gerais.

Publication Dates

• Publication in this collection
  16 Oct 2020
• Date of issue
  Jul-Sep 2020

History

• Received
  09 Apr 2020
• Accepted
  26 June 2020