INTRODUCTION
Senna Miller 1754 (Fabaceae) comprises a diverse group of flowering plants with several of its species known for their medicinal properties and ornamental use (Marazzi and Sanderson, 2010). It has about 250–300 accepted species of tree shrubs and subshrubs dispersed in tropical and subtropical regions, with about 80% distributed in the American region (Irwin and Barneby, 1982; Oladeji et al., 2021; Alshehri et al., 2022). Folk medicine has utilized several of the Senna species as purgatives as they contain anthraquinone derivatives and glucosides, sennosides or senna glycosides (Monkheang et al., 2011; Rahman et al., 2013).
In the Philippines, 11 Senna species have been documented: S. alata (L.) Roxb., S. divaricata (Nees & Blume) Lock, S. fruticosa (Mill.) H. S. Irwin & Barneby, S. hirsuta (L.) H. S. Irwin & Barneby, S. obtusifolia (L.) H. S. Irwin & Barneby, S. occidentalis (L.) Link, S. siamea (Lam.) H. S. Irwin & Barneby, S. spectabilis (DC.) H. S. Irwin & Barneby, S. timoriensis (DC.) H. S. Irwin & Barneby, and S. tora (L.) Roxb. (Pelser et al., 2025). Among these, S. alata, also known as ‘akapulko’, is the only species recognized and endorsed by the Department of Health as one of the ten medicinal plants, valued for its antifungal and dermatological applications (Philippine Pharmacopeia 1, 2004). Its ability to grow in diverse environments and disturbed habitats caused it to be classified also as a weedy species despite widespread cultivation and the potential of its bioactive molecules. The characterization of its taxonomy and other Senna species remains locally understudied with limited morphological and molecular studies available to confirm species identities beyond S. alata.
In the southern Philippines, particularly in the Zamboanga Peninsula, local communities refer to a similar-looking plant as ‘asunting’. This plant exhibits key morphological traits that differ from S. alata such as its pod structure and leaf characters. This local ‘asunting’ have plano-compressed, unwinged pods which are morphological traits of S. reticulata (Willd.) H. S. Irwin & Barneby as described in The American Cassiinae (1982). Native to South America, S. reticulata is a fast-growing species known for its ability to colonize riparian zones and disturbed landscapes. Its rapid growth has been proposed for its potential biomass source for bioenergy production (Grandis et al., 2021). The species has also been recorded to be introduced and cultivated in India (Parolin et al., 2002), but the lack of proper documentation of its identity raises the question on whether the species cultivated is genuinely S. reticulata. Its presence in the Philippines has not been previously documented in floristic accounts which raises questions about its origin, mode of introduction, and ecological impact in Zamboanga (Pelser et al., 2025; POWO, 2025).
Thus, to clarify the taxonomy of this potentially introduced species, we employed an integrative approach to species identification. We also documented its distribution through a rapid inventory conducted along the roadsides and national highway to trace its occurrence and establishment in Zamboanga Peninsula.
MATERIALS AND METHODS
Plant material
The plant material was collected in Philippine Rubber Research Institute (PRRI), Zamboanga Sibugay, and along the roadsides of the Pan-Philippine National Highway, Tigbao, Zamboanga del Sur (7°83′15″N, 123°23′83″E) in January 2025.
Herbarium
Local collections of Senna alata (ICROPS) were revisited and examined to ensure accurate identification. Herbarium specimens housed at the Philippine University Herbarium (PUH) in the University of the Philippines – Diliman, Philippine National Herbarium (PNH), and Singapore Herbarium National Parks Board (SING) were also observed. The voucher specimens (ICROPS 0012025001, ICROPS 0012025002, ICROPS 0012025003) were prepared and deposited at the Philippine Herbarium of Cultivated Plants, Institute of Crop Science, University of the Philippines Los Baños (https://cafs.uplb.edu.ph/icrops/; Curator: Dr. Renerio P. Gentallan Jr., rpgentallan@up.edu.ph).
Morphological characterization
The morphology of the Senna sp. accession was examined using diagnostic morphological markers described for the Senna group in The American Cassiinae monograph (Irwin and Barneby, 1982) to confirm the sample’s identity. It was characterized following the modified Senna alata descriptor list developed by the Crop Breeding and Genetic Resources Laboratory, Institute of Crop Science, College of Agriculture and Food Science, University of the Philippines Los Baños. Ten replicates were used to measure 11 quantitative characteristics. A key to the Philippine Senna species was devised following the descriptions provided in The American Cassiinae by Irwin and Barneby (1982), Flora Malesiana (Hou et al., 1996), and Flora e Funga do Brasil (2025).
DNA extraction and sequencing
The study utilized disease-free leaves of a mature Senna sp. (ICROPS 0012025002). The leaves were pre-dried using silica drying method, and DNA was extracted following the liquid-nitrogen-free CTAB protocol described by Quiñones et al. (2024). Chloroplast and nuclear barcode sequence amplification was done using sequence-specific markers (Table 1) at 94°C for 5 min; 30 cycles of 94°C for 45 s, 55°C for 45 s, and 72°C for 1 min, and 72°C for 7 min, using a thermal cycler (Bio-Rad T100, Hercules, CA, USA).
The PCR products were subsequently sent to Macrogen Inc. (Seoul, Korea) for purification and capillary (Sanger) sequencing. The sequences derived from capillary sequencing subjected to end clipping using Geneious Prime 2024. A nucleotide BLAST (BLASTn) search was conducted using the cleaned sequences to compare them with existing nucleotide sequences in GenBank at National Center for Biotechnology Information (NCBI). The rbcL and internal transcribed spacer (ITS) sequence data that support the findings of this study are openly available in GenBank of NCBI at www.ncbi.nlm.nih.gov under accession no. PX121432 and PV796072, respectively.
Phylogenetic analysis
Forty-six ITS sequences from NCBI were downloaded to serve as ingroup (38 Senna species), sister group (three Cassia species) and outgroup (five related species) under the Umtiza clade of the subfamily Caesalpinioideae in the phylogenetic analysis.
The selection of taxa included in the phylogenetic analysis of the nuclear marker was primarily based on the species utilized by Ringelberg et al. (2022) in their phylogenomic analysis of Caesalpinioideae (Leguminosae) and the new subfamily classification of the Leguminosae based on a taxonomically comprehensive phylogeny by The Legume Phylogeny Working Group (2017). These sequences, along with the partial ITS sequence of ICROPS 0012025002, were aligned using MAFFT (Katoh and Standley, 2013) and, after alignment trimming, phylogenetic analysis was performed using MEGA 12 (Kumar et al., 2024). The model with the lowest Bayesian information criterion score was selected. The phylogenetic tree was generated using the maximum likelihood method following the general time reversible, gamma-invariant (GTR + G + I) model at 1,000 bootstrap replicates.
Distribution mapping
Thirty-one coordinates were recorded as occurrence points of Senna sp. through rapid field inspection in 2025 en route to Zamboanga Sibugay. Closer inspection of the distinct growth habit, leaf, and pod morphology between S. reticulata and S. alata was done to ensure proper identification. To verify and supplement these data with historical records, the initial 31 coordinates were re-examined using Google Maps Street View imagery from 2016 and 2022. Potential populations were visually confirmed by the presence of previously identified stands observable at street level. The GPS coordinates of each verified location were compiled into a CSV file for spatial analysis. The map was generated using QGIS 3.44.0 to visualize its distribution.
RESULTS AND DISCUSSION
Morphological characterization
Three dried specimens (ICROPS 0012025001, ICROPS 0012025002, ICROPS 0012025003) were prepared and examined. Key morphological traits such as the petiole length, leaflet pilosity, and pod shape remained distinctly identifiable after drying and were consistent with the diagnostic features of S. reticulata as described by Irwin and Barneby (1982). The morphology of the examined specimen was depicted in Fig. 1. Morphological characterization of the collected Senna sp. revealed at least seven diagnostic traits aligning with the description of Senna reticulata (Willd.) H. S. Irwin & Barneby and clearly distinguishing it from S. alata (‘akapulko’) (Table 2). The specimen exhibited a petiole length of 12.57 ± 0.88 cm which exceeds the upper range typically observed in S. alata (1–3.5 cm) and falls within the range described for S. reticulata (3.5–13 cm). The seta at the rachis base was dilated into a lance-triangular blade measuring approximately 3.75 ± 0.09 mm, a trait also characteristic of S. reticulata but often subobsolete in S. alata, where the first leaflet pair is inserted near the pulvinus. The leaflets of the specimen were pilosulous-puberulent on both upper and lower surfaces, whereas S. alata typically exhibits glabrous upper leaflet surfaces and sparse hairs limited to the lower veins.
The pod morphology was the definitive delineating character upon first field observation. The examined specimen had plano-compressed and unwinged pods (Fig. 1I) unlike S. alata which bears four-angular, winged pods. Mainly, the pod compression, pilosity, and elongate petiole strongly support the identification of the specimen based on morphologic features as S. reticulata rather than S. alata. The floral morphology needs to be further assessed in future studies to strengthen this identification.
Parolin (2001) referred to Senna reticulata as a pioneer tree native to the Amazonian várzea floodplains and described it as having glabrous leaflets on both surfaces, crenulated-winged pods, and petioles lacking glands. However, these morphological features more closely correspond to Senna alata based on the taxonomic treatment by Irwin and Barneby (1982). The description of Parolin (2001) thus treats S. reticulata and S. alata as the same species. In contrast, the specimen examined in this study exhibits diagnostic traits consistent with the description for S. reticulata as a species distinct from S. alata.
Molecular characterization and phylogenetic analysis
A 608-bp partial rbcL sequence was successfully generated. BLAST analysis against the NCBI nucleotide database revealed a 100% identity and 100% query coverage with a single accession of Senna reticulata (NC_083217.1), despite the presence of over 66 rbcL sequences from various Senna species. This unequivocally supports the identification of the specimen as S. reticulata. When compared with the published S. alata reference sequence (Quiñones et al., 2023), the sequenced region contained six variable nucleotide sites.
In contrast, analysis of a 693-bp partial ITS sequence showed the highest similarity to S. alata (97.03% identity). However, this result is inconclusive, owing to the absence of S. reticulata ITS sequences in GenBank and the sub-threshold identity of the closest taxon. To further assess this, phylogenetic analysis was performed to determine whether the ITS sequence would recover the same topology as that inferred from literature. The ITS alignment spanned 700 bp, with 436 variable sites (62.29%) and 321 parsimony-informative characters (45.86%). In the resulting ITS-based phylogram, the putative S. reticulata accession (ICROPS 0012025002) grouped closely with S. alata with moderate bootstrap support (Fig. 2), consistent with the evolutionary relationship reported by Marazzi et al. (2006) based on three chloroplast markers (rps16, rpl16, and matK). The overall topology of the ITS tree also corresponds well with those recovered in more recent phylogenetic studies (The Legume Phylogeny Working Group, 2017; Ringelberg et al., 2022; Quiñones et al., 2023).
Taken together, the congruence of chloroplast and nuclear molecular evidence reinforces the morphological identification of the specimen as Senna reticulata.
Rapid local establishment
The highest density of occurrences was documented along the Maria Clara Lorenzo Lobregat Highway in Zamboanga City with over 30 closely spaced GPS points from the location coordinates recorded from 2016 and 2022 (Fig. 3). This section of the national highway consists of unmanaged roadside vegetation where populations of Senna species are established. A more scattered distribution was observed along AH26 in Tungawan extending toward the Pagadian City–Zamboanga City Road in Roseller T. Lim and Ipil, Zamboanga Sibugay. This indicates a wider distribution of the species within the region. Field observations in 2025, together with historical Google Maps imagery (2016–2022), revealed population increase of the species over the six-year observable period, suggesting rapid local establishment up to the present. While formal monitoring has not yet been conducted, the sustained and widespread presence in disturbed habitats suggests the species may have the potential to naturalize in the area.
Senna reticulata was observed forming dense stands along roadsides, agricultural fields, and riverbanks, primarily in disturbed secondary vegetation within the study area. Based on current floristic records (POWO, 2025), this species is not native to the Philippines and is considered a newly introduced species. Field observations documented its establishment in fallow agricultural land and its capacity to form dense thickets. Local reports also noted difficulty in eradicating established individuals (PRRI staff, pers. comm.). Ecologically, S. reticulata exhibits traits commonly associated with invasive species, including rapid growth (reaching up to ~4 m within months), the ability to form dense, monospecific stands, tolerance to seasonal flooding, and vigorous vegetative regrowth following disturbance—traits well-documented in Amazonian várzea ecosystems (Parolin, 2001).
Its presence in the Philippines has not been previously documented in floristic accounts (Blanco, 1845; Merrill, 1923; Hou et al., 1996; Pelser et al., 2023; iNaturalist, 2025a, 2025b). Additionally, there were no records of the species in local and international herbaria (PNH, PUH, SING), suggesting its recent introduction. Based on its characteristics and its observed presence in the region, several potential introduction pathways can be hypothesized. One possibility is its intentional introduction as an ornamental plant or for use in traditional medicine, as it bears a strong resemblance to the widely cultivated Senna alata (‘akapulko’/’asunting’). Another possibility is an unintentional introduction, where the seeds or other plant material were introduced as a contaminant in agricultural products or through human-mediated transport. This hypothesis is supported by the species’ rapid growth and ability to colonize disturbed landscapes, such as roadsides, riverbanks, and fallow agricultural lands, where it forms dense stands. While the specific route of introduction remains unknown, the species may pose a threat to native plant communities and warrants formal evaluation under national invasive species monitoring frameworks given its alien status, progressive colonization, and ecological traits.
Taxonomic Treatment
Senna reticulata (Willd.) H. S. Irwin & Barneby, Mem. New York Bot. Gard. 35: 458, 1982.
Description: Habit shrub to small tree. Stems with fine, short, or soft hairs. Stipules lanceolate to triangular. Leaves with petiole (9–)10–13(−16) cm long; rachis >21 cm long; extrafloral nectary absent. Leaflets 6–10 pairs, oblong, (9−)10–11 × 3–4 cm, apex round. Inflorescence yellow raceme; bracts ovate. Flowers zygomorphic; central upper petal obovate; fertile stamens 6. Pods flat, black, pendulous, long-linear, 11–12 × (1.3−)1.4–1.5 cm. Seeds 1-seriate, brown, 7–8 × 2–4 × 1–2 mm.
Origin: South Mexico, Trinidad, South America (POWO, 2025).
Introduced: Zamboanga city, Zamboanga del Sur, and Zamboanga Sibugay, Philippines (this study).
Habitat and ecology: This shrub thrives in disturbed areas, roadsides, riverbanks, and near paddy fields.
Specimens examined (Fig. 4): Philippines. Zamboanga Sibugay, 2025, Pasamba, Gentallan, Timog, Hernandez 0012025001 (ICROPS); Zamboanga Sibugay, 2025, Pasamba, Gentallan, Timog, Hernandez 0012025002 (ICROPS); Zamboanga Sibugay, 2025, Remollo 0012025003 (ICROPS).
Other specimens examined (Senna alata):
Philippines. Luzon–Batanes: Batan Island, 1961, Quisumbing, del Rosario & Guiterrez 79259 (PNH). Bataan: Pilar, 1954, Banzon 3542 (PUH); Lamao River, Mt. Mariveles, 1905, Meyer 2583 (SING); Lamao River, Mt. Mariveles, 1904, Meyer 2198 (SING). Bulacan: Balintawak Km. 8, 1946, Mendoza 3076 (PNH). Ilocos Norte: Sto. Niño, 1983, Vendivil & Reynoso 160625 (PNH); Sto. Niño, 1983, Vendivil & Reynoso 160636 (PNH). Laguna: Mt. Makiling, 1945, Sulit 8332 (PNH); Bo Kapatalan Siniloan, 230 m, 1971, Francia 5779 (PUH). Manila: Manila, 1906, McGregor 1743 (SING). Palawan: Taripan, 40m, 1962, Fox 154625 (PNH). Mindoro: Calagbay, 1939, Ebalo 57455 (PNH); Bongabon & Pinamalayan, 1941, Maliwanag 57218 (PNH); NE of Mt. Yagaw, Oriental Mindoro, 1957, Conklin 37579 (SING). Palawan: Baraki, 500 m, 1950, Fox 13365 (PNH); Lipso, 15 m, 1984, Holol 150965 (PNH). Quezon: Kinagunan Ibaba, Agdangan, 1976, Francisco 170824 (PNH); Mt. Binayabas, Atimonan, 1977, Vendivil & Reynoso 169437 (PNH). Rizal: 1946, Quisumbing 2107 (PNH). Zambales: Sta. Rita, Masinloc, 1977, dela Cruz & Fernando 123522 (PNH). Visayas–Iloilo: San Joaquin, 1953, Taleon 22393 (PNH). Mindanao–Agusan: Mt. Hilonghilong, 830 m, 1949, Mendoza & Convocan 10687 (PNH). Cagayan: Solana, 1980, Rocero 152842 (PNH). Mindanao–Davao: Digos, 1950, Añonuevo 13690 (PNH). Sulu: Taganak Island, 1957, Kondo & Edaño 38888 (PNH). Zamboanga del Sur: Lapuyan, 1984, Filomena 159953 (PNH). Zamboanga Sibugay: Mt. Kumayo, 1940, Ebalo 57687 (PNH).
Vernacular names: akapulko (Tag./Bis.), asunting (Bis.).
Taxonomic note: Based on our morphological and molecular data, we confirm the first known record of the Senna reticulata in the Philippines. The unrecorded species discussed here is locally referred to as ‘akapulko’ or ‘asunting’. It is known for its antifungal properties. Its late detection in the area may be attributed to its confusion with S. alata as these two species are often referred to by the same vernacular name and used interchangeably in traditional medicine due to their resemblance in appearance, growth form, and medicinal properties. Examination of Senna herbarium collections in the Philippines revealed no verifiable specimens of S. reticulata, suggesting that it may be a recent introduction.
Population of the species was observed along the roadside from Zamboanga del Sur to Zamboanga Sibugay. The species thrives in disturbed and open conditions. Irwin and Barneby (1982) described the species as seldom forming extensive thickets; however, the population observed was densely established along the national highway.
Key to the Senna species in the Philippines
-
1. Glands absent from both petioles and rachis.
-
2. Pedicels shorter than sepals.
3. Rachis ending in slender seta; leaflets usually glabrous above, petiole ≤ 3.5 cm long; pods sharply four-angular, winged ········································································································································ S. alata
3. Rachis ending in dilated deltate or lance-triangular blade; leaflets pilose, petiole > 3.5 cm long; pods plano-compressed, not winged ····················································································································· S. reticulata
-
2. Pedicels longer than sepals.
-
-
1. Glands present on either petioles or rachis.
PDF Links
PubReader
ePub Link
Full text via DOI
Download Citation 
Print 
