Materials and methods

Taxon sampling

All specimens were collected during several field campaigns in Thailand from 2005 through 2010. Identifications were based on the keys and descriptions in Cheesman (1948), Simmonds (1956, 1962), De Langhe and Devreux (1960), and De Langhe et al. (2000). A total of 211 accessions of Musa acuminata Colla sensu lato were studied, all of which were collected in natural habitats (Suppl. material 1). The outgroup comprised three accessions of wild M. itinerans Cheesman and six accessions of wild M. rubra. All reference collections were deposited at the SLR Herbarium in Bangkok (Holmgren et al. 1990). The voucher specimens included the apical part of the inflorescence (male flowers) and fruits preserved in alcohol, as well as the base, middle, and apex of an untorn mature leaf. Morphological descriptions were prepared on-site using a standardized format that integrated the diagnostic features suggested by Simmonds and Shepherd (1955), De Langhe and Devreux (1960), Simmonds (1962), Argent (1976), and Nasution (1991) and are available from the authors. Colors were determined using the IPGRI-INIBAP/CIRAD color chart for bananas (IPGRI-INIBAP/CIRAD 1996). All accessions were geolocated with a handheld GPS tracker. The circumscriptions of floristic regions and provinces (Changwats) follow those of the Flora of Thailand project (1970–2026) (Suppl. material 1; Fig. 1).

Figure 1.: Distribution of the four subspecies of Musa acuminata across the floristic provinces of Thailand (Northern, North-eastern, Eastern, South-western, Central, South-eastern, and Peninsular). Symbols represent records of each subspecies.

Morphological analysis

A total of 16 morphological characters were scored in the field for 195 accessions. The characters were divided into states, as shown in Table 1, Suppl. material 2. Similarity coefficients were then calculated using PAST 4.05 (Hammer et al. 2001). All characters used in the analyses were equally weighted. The cluster analysis combined Gower’s distance measure with the unweighted pair-group method using arithmetic averages (UPGMA). Diagnostically useful characters for distinguishing subspecies of M. acuminata were derived by maximum parsimony mapping of character states onto the resulting dendrogram.

# | Characters | State 1 | State 2 | State 3 | State 4 | State 5
1 | Petiolar canal | Open with margin spreading | Wide with erect margins | Straight with erect margins | Margins curved inward | Margins overlapping
2 | Leaf base | Cuneate | Oblique | Round | Cordate | Auriculate
3 | Peduncle and rachis color | Green | Purplish brown to dark purple |  |  | 
4 | Bunch direction | Horizontal to angle | Erect |  |  | 
5 | Number of rows in fruit hand | Uniseriate | Biseriate |  |  | 
6 | Rachis diameter | Slender (Diameter less than 2.5 cm) | Thick (diameter more than 2.5 cm) |  |  | 
7 | Rachis direction | Hanging vertically | At an angle | With a curve | Horizontal | Erect
8 | Direction of inflorescence apex in the male phase | Vertically | Downward | Upward | Erect | 
9 | Male-phase inflorescence number | One | Numerous |  |  | 
10 | Bud shape | Ovate | Elliptic-ovate |  |  | 
11 | Arrangement of the rachis bracts | Greatly overlap | Slightly overlap | Non-overlap |  | 
12 | Inside (adaxial) color of the rachis bracts | Pink purple, red purple, orange red | Yellow | Ivory | Orange | 
13 | Outside (abaxial) color of the rachis bracts | Orange red, red, purple red, red purple, dark purple, purple brown | Orange | Yellow |  | 
14 | Shoulders of free tepal | Entire | Incised |  |  | 
15 | Fruit shape | Tubular | Fusiform |  |  | 
16 | Seed surface | Smooth | Rough |  |  |